1 Introduction

The web services framework, has, in essence, begun to create a standard software “communications bus” in support of service-oriented architecture. Applications and services can “plug in” to the bus and begin communicating using standards tools. The emergence of this “bus” has profound implications for identity exchange.

Jamie Lewis, Burton Group, February 2005
Forward to Digital Identity by Phillip J. Windley

As noted by Jamie Lewis, the emergence of web services as a common communications bus has “profound implications.” The next generation of biometric devices will not only need to be intelligent, secure, tamper-proof, and spoof resistant, but first, they will need to be interoperable.

These envisioned devices will require a communications protocol that is secure, globally connected, and free from requirements on operating systems, device drivers, form factors, and low-level communications protocols. WS-Biometric Devices is a protocol designed in the interest of furthering this goal, with a specific focus on the single process shared by all biometric systems—acquisition.

1.1 Terminology

This section contains terms and definitions used throughout this document. First time readers may desire to skip this section and revisit it as needed.

biometric capture device

a system component capable of capturing biometric data in digital form

client

a logical endpoint that originates operation requests

HTTP

Hypertext Transfer Protocol. Unless specified, the term HTTP refers to either HTTP as defined in [RFC2616] or HTTPS as defined in [RFC2660].

ISO

International Organization for Standardization

modality

a distinct biometric category or type of biometric—typically a short, high-level description of a human feature or behavioral characteristic (e.g., “fingerprint,” “iris,” “face,” or “gait”)

payload

the content of an HTTP request or response. An input payload refers to the XML content of an HTTP request. An output payload refers to the XML content of an HTTP response.

payload parameter

an operation parameter that is passed to a service within an input payload

profile

a list of assertions that a service must support

REST

Representational State Transfer

RESTful

a web service which employs REST techniques

sensor or biometric sensor

a single biometric capture device or a logical collection of biometric capture devices

SOAP

Simple Object Access Protocol

submodality

a distinct category or subtype within a biometric modality

target sensor or target biometric sensor

the biometric sensor made available by a particular service

URL parameter

a parameter passed to a web service by embedding it in the URL

Web service or service or WS

a software system designed to support interoperable machine-to-machine interaction over a network [WSGloss]

XML

Extensible Markup Language [XML]

1.2 Documentation Conventions

The following documentation conventions are used throughout this document.

1.2.1 Key Words

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in[RFC2119].

1.2.2 Quotations

If the inclusion of a period within a quotation might lead to ambiguity as to whether or not the period should be included in the quoted material, the period will be placed outside the trailing quotation mark. For example, a sentence that ends in a quotation would have the trailing period “inside the quotation, like this quotation punctuated like this.” However, a sentence that ends in a URL would have the trailing period outside the quotation mark, such as “http://example.com”.

1.2.3 Machine-Readable Code

With the exception of some reference URLs, machine-readable information will typically be depicted with a mono-spaced font, such as this.

1.2.4 Sequence Diagrams

Throughout this document, sequence diagrams are used to help explain various scenarios. These diagrams are informative simplifications and are intended to help explain core specification concepts. Operations are depicted in a functional, remote procedure call style.

The following is an annotated sequence diagram that shows how an example sequence of HTTP request-responses is typically illustrated. The level of abstraction presented in the diagrams, and the details that are shown (or not shown) will vary according to the particular information being illustrated. First time readers may wish to skip this section and return to it as needed.

Figure 1. Example of a sequence diagram used in this document.

1. Each actor in the sequence diagram (i.e., a client or a server) has a “swimlane” that chronicles their interactions over time. Communication among the actors is depicted with arrows. In this diagram, there are three actors: “Client A,” a WS-BD “Service,” and “Client B.”

2. State information notable to the example is depicted in an elongated diamond shape within the swimlane of the relevant actor. In this example, it is significant that the initial “lock owner” for the “Service” actor is “(none)” and that the “lock owner” changes to “{A1234567…}” after a communication from Client A.

3. Unless otherwise noted, a solid arrow represents the request (initiation) of an HTTP request; the opening of an HTTP socket connection and the transfer of information from a source to its destination. The arrow begins on the swimlane of the originator and ends on the swimlane of the destination. The order of the request and the operation name (§6.3 through §6.16) are shown above the arrow. URL and/or payload parameters significant to the example are shown below the arrow. In this example, the first communication occurs when Client A opens a connection to the Service, initiating a “lock” request, where the “sessionId” parameter is “{A1234567…}.”

4. Unless otherwise noted, a dotted arrow represents the response (completion) of a particular HTTP request; the closing of an HTTP socket connection and the transfer of information back from the destination to the source. The arrow starts on the originating request’s destination and ends on the swimlane of actor that originated the request. The order of the request, and the name of the operation that being replied to is shown above the arrow. Significant data “returned” to the source is shown below the arrow (§3.13.1). Notice that the source, destination, and operation name provide the means to match the response corresponds to a particular request—there is no other visual indicator. In this example, the second communication is the response to the “lock” request, where the service returns a “status” of “success.”

In general, “{A1234567…}” and “{B890B123…}” are used to represent session ids (§2.4.3, §3.13.3, §6.3); “{C1D10123...}” and “{D2E21234...}” represent capture ids (§3.13.3, §6.12).

1.3 Normative References

[3GPP]	3GPP, 3GPP TS 26.244 Transparent end-to-end packet switched streaming service (PSS) 3GPP file format (3GP), http://www.3gpp.org/DynaReport/26244.htm, Retrieved 12 August 2014
[3GPP2]	3GPP2, C.S0050-B Version 1.0 3GPP2 File Formats for Multimedia Services, http://www.3gpp2.org/Public_html/specs/C.S0050-B_v1.0_070521.pdf, 18 May 2007
[AIFF]	Apple Computer, Inc., Audio Interchange File Format: "AIFF". A Standard for Sampled Sound Files Version 1.3, http://www-mmsp.ece.mcgill.ca/Documents/AudioFormats/AIFF/Docs/AIFF-1.3.pdf, January 4, 1989
[AN2K]	Information Technology: American National Standard for Information Systems—Data Format for the Interchange of Fingerprint, Facial, & Scar Mark & Tattoo (SMT) Information, http://www.nist.gov/customcf/get_pdf.cfm?pub_id=151453, 27 July 2000.
[AN2K11]	B. Wing, Information Technology: American National Standard for Information Systems—Data Format for the Interchange of Fingerprint, Facial & Other Biometric Information, http://www.nist.gov/customcf/get_pdf.cfm?pub_id=910136, November 2011.
[AN2K7]	R. McCabe, E. Newton, Information Technology: American National Standard for Information Systems—Data Format for the Interchange of Fingerprint, Facial, & Other Biometric Information – Part 1, http://www.nist.gov/customcf/get_pdf.cfm?pub_id=51174, 20 April 2007.
[AN2K8]	E. Newton et al., Information Technology: American National Standard for Information Systems—Data Format for the Interchange of Fingerprint, Facial, & Other Biometric Information – Part 2: XML Version, http://www.nist.gov/customcf/get_pdf.cfm?pub_id=890062, 12 August 2008.
[ASF]	Overview of the ASF Format, http://msdn.microsoft.com/en-us/library/windows/desktop/dd757562%28v=vs.85%29.aspx, Retrieved 13 August 2014
[ASX]	Windows Media Metafile Elements Reference, http://msdn.microsoft.com/en-us/library/dd564668%28VS.85%29.aspx, Retrieved 13 August 2014
[AVI]	AVI RIFF File Format, http://msdn.microsoft.com/en-us/library/ms779636.aspx, Retrieved 12 August 2014
[BDIF1007]	ISO/IEC 19794-10:2007: Information technology – Biometric data interchange formats – Part 10: Hand geometry silhouette data
[BDIF205]	ISO/IEC 19794-2:2005/Cor 1:2009/Amd 1:2010: Information technology – Biometric data interchange formats – Part 2: Finger minutia data
[BDIF306]	ISO/IEC 19794-3:2006: Information technology – Biometric data interchange formats – Part 3: Finger pattern spectral data
[BDIF405]	ISO/IEC 19794-4:2005: Information technology – Biometric data interchange formats – Part 4: Finger image data
[BDIF505]	ISO/IEC 19794-5:2005: Information technology – Biometric data interchange formats – Part 5: Face image data
[BDIF605]	ISO/IEC 19794-6:2005: Information technology – Biometric data interchange formats – Part 6: Iris image data
[BDIF611]	ISO/IEC 19794-6:2011: Information technology – Biometric data interchange formats – Part 6: Iris image data
[BDIF707]	ISO/IEC 19794-7:2007/Cor 1:2009: Information technology – Biometric data interchange formats – Part 7: Signature/sign time series data
[BDIF806]	ISO/IEC 19794-8:2006/Cor 1:2011: Information technology – Biometric data interchange formats – Part 8: Finger pattern skeletal data
[BDIF907]	ISO/IEC 19794-9:2007: Information technology – Biometric data interchange formats – Part 9: Vascular image data
[BMP]	BMP File Format, http://www.digicamsoft.com/bmp/bmp.html
[CBEFF2010]	ISO/IEC 19785-3:2007/Amd 1:2010: Information technology – Common Biometric Exchange Formats Framework – Part 3: Patron format specifications with Support for Additional Data Elements
[CMediaType]	Media Types, http://www.iana.org/assignments/media-types/media-types.xhtml, 8 August 2014
[H264]	Y.-K. Wang et al., RTP Payload Format for H.264 Video, http://www.ietf.org/rfc/rfc6184.txt, IETF RFC 6184, May 2011.
[HTML5]	HTML5. A vocabulary and associated APIs for HTML and XHTML. W3C Candidate Recommendation, http://www.w3.org/TR/html5/, 31 July 2014.
[JPEG]	E. Hamilton, JPEG File Interchange Format, http://www.w3.org/Graphics/JPEG/jfif3.pdf, 1 September 1992.
[MPEG]	ISO/IEC 14496: Information technology – Coding of audio-visual objects
[MPEG1]	ISO/IEC 11172-3:1993/Cor 1:1996 Information technology – Coding of moving pictures and associated audio for digital storage media at up to about 1.5 Mbit/s -- Part 3: Audio
[OGG]	Xiph.org, http://xiph.org/ogg/, Retrieved 12 August 2014
[PNG]	D. Duce et al., Portable Network Graphics (PNG) Specification (Second Edition), http://www.w3.org/TR/2003/REC-PNG-20031110, 10 November 2003.
[QTFF]	Introduction to Quicktime File Format Specification, https://developer.apple.com/library/mac/documentation/QuickTime/QTFF/QTFFPreface/qtffPreface.html, Retrieved 12 August 2014
[RFC1737]	K. Sollins, L. Masinter, Functional Requirements for Uniform Resource Names, http://www.ietf.org/rfc/rfc1737.txt, IETC RFC 1737, December 1994.
[RFC2045]	N. Freed and N. Borenstein, Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies, http://www.ietf.org/rfc/rfc2045.txt, IETF RFC 2045, November 1996.
[RFC2046]	N. Freed and N. Borenstein, Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types, http://www.ietf.org/rfc/rfc2046.txt, IETF RFC 2045, November 1996.
[RFC2119]	S. Bradner, Key words for use in RFCs to Indicate Requirement Levels, http://www.ietf.org/rfc/rfc2119.txt, IETF RFC 2119, March 1997.
[RFC2141]	R. Moats, URN Syntax, http://www.ietf.org/rfc/rfc2141.txt, IETF RFC 2141, May 1997
[RFC2616]	R. Fielding, et al., Hypertext Tranfer Protocol—HTTP/1.1, http://www.ietf.org/rfc/rfc2616.txt, IETF RFC 2616, June 1999.
[RFC2660]	E. Rescorla et al., The Secure HyperText Transfer Protocol, http://www.ietf.org/rfc/rfc2660.txt, IETF RFC 2660, August 1999.
[RFC3001]	M. Mealling, A URN Namespace of Object Identifiers, http://www.ietf.org/rfc/rfc3001.txt, IETF RFC 3001, November 2000.
[RFC4122]	P. Leach, M. Mealling, and R. Salz, A Universally Unique Identifier (UUID) URN Namespace, http://www.ietf.org/rfc/rfc4122.txt, IETF RFC 4122, July 2005.
[SPHERE]	National Institute of Standards and Technology, NIST Speech Header Resources, http://www.nist.gov/itl/iad/mig/tools.cfm, Retrieved 12 August 2014
[TIFF]	TIFF Revision 6.0, http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf, 3 June 1992.
[WAVE]	IBM Corporation and Microsoft Corporation, Multimedia Programming Interface and Data Specifications 1.0, http://www.tactilemedia.com/info/MCI_Control_Info.html, August 1991
[WSGloss]	H. Haas, A. Brown, Web Services Glossary, http://www.w3.org/TR/2004/NOTE-ws-gloss-20040211/, February 11, 2004.
[WSQ]	WSQ Gray-Scale Fingerprint Image Compression Specification Version 3.1, https://fbibiospecs.org/docs/WSQ_Gray-scale_Specification_Version_3_1_Final.pdf, 4 October 2010.
[XML]	Tim Bray et al., Extensible Markup Language (XML) 1.0 (Fifth Edition), http://www.w3.org/TR/xml/. W3C Recommendation. 26 November 2008.
[XMLNS]	Tim Bray et al., Namespace in XML 1.0 (Third Edition), http://www.w3.org/TR/2009/REC-xml-names-20091208/. W3C Recommendation. 8 December2009.
[XSDPart1]	Henry Thompson et al., XML Schema Part 1: Structures Second Edition, http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/, W3C Recommendation. 28 October 2004.
[XSDPart2]	P. Biron, A. Malhotra, XML Schema Part 2: Datatypes Second Edition, http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/, W3C Recommendation. 28 October 2004.

2 Design Concepts and Architecture

This section describes the major design concepts and overall architecture of WS-BD. The main purpose of a WS-BD service is to expose a target biometric sensor to clients via web services.

This specification provides a framework for deploying and invoking core synchronous operations via lightweight web service protocols for the command and control of biometric sensors. The design of this specification is influenced heavily by the REST architecture; deviations and tradeoffs were made to accommodate the inherent mismatches between the REST design goals and the limitations of devices that are (typically) oriented for a single-user.

2.1 Interoperability

ISO/IEC 2382-1 (1993) defines interoperability as “the capability to communicate, execute programs, or transfer data among various functional units in a manner that requires the user to have little to no knowledge of the unique characteristics of those units.”

Conformance to a standard does not necessarily guarantee interoperability. An example is conformance to an HTML specification. A HTML page may be fully conformant to the HTML 4.0 specification, but it is not interoperable between web browsers. Each browser has its own interpretation of how the content should be displayed. To overcome this, web developers add a note suggesting which web browsers are compatible for viewing. Interoperable web pages need to have the same visual outcome independent of which browser is used.

A major design goal of WS-BD is to maximize interoperability, by minimizing the required “knowledge of the unique characteristics” of a component that supports WS-BD. The authors recognize that conformance to this specification alone cannot guarantee interoperability; although a minimum degree of functionality is implied. Sensor profiles and accompanying conformance tests will need to be developed to provide better guarantees of interoperability, and will be released in the future.

2.2 Architectural Components

Before discussing the envisioned use of WS-BD, it is useful to distinguish between the various components that comprise a WS-BD implementation. These are logical components that may or may not correspond to particular physical boundaries. This distinction becomes vital in understanding WS-BD’s operational models.

2.2.1 Client

A client is any software component that originates requests for biometric acquisition. Note that a client might be one of many hosted in a parent (logical or physical) component, and that a client might send requests to a variety of destinations.

This icon is used to depict an arbitrary WS-BD client. A personal digital assistant (PDA) is used to serve as a reminder that a client might be hosted on a non-traditional computer.

2.2.2 Sensor

A biometric sensor is any component that is capable of acquiring a digital biometric sample. Most sensor components are hosted within a dedicated hardware component, but this is not necessarily globally true. For example, a keyboard is a general input device, but might also be used for a keystroke dynamics biometric.

This icon is used to depict a biometric sensor. The icon has a vague similarity to a fingerprint scanner, but should be thought of as an arbitrary biometric sensor.

The term “sensor” is used in this document in a singular sense, but may in fact be referring to multiple biometric capture devices. Because the term “sensor” may have different interpretations, practitioners are encouraged to detail the physical and logical boundaries that define a “sensor” for their given context.

2.2.3 Sensor Service

The sensor service is the “middleware” software component that exposes a biometric sensor to a client through web services. The sensor service adapts HTTP request-response operations to biometric sensor command & control.

This icon is used to depict a sensor service. The icon is abstract and has no meaningful form, just as a sensor service is a piece of software that has no physical form.

2.3 Intended Use

Each implementation of WS-BD will be realized via a mapping of logical to physical components. A distinguishing characteristic of an implementation will be the physical location of the sensor service component. WS-BD is designed to support two scenarios:

1. Physically separated. The sensor service and biometric sensor are hosted by different physical components. A physically separated service is one where there is both a physical and logical separation between the biometric sensor and the service that provides access to it.

2. Physically integrated. The sensor service and biometric sensor are hosted within the same physical component. A physically integrated service is one where the biometric sensor and the service that provides access to it reside within the same physical component.

Figure 2 depicts a physically separated service. In this scenario, a biometric sensor is tethered to a personal computer, workstation, or server. The web service, hosted on the computer, listens for communication requests from clients. An example of such an implementation would be a USB fingerprint scanner attached to a personal computer. A lightweight web service, running on that computer could listen to requests from local (or remote) clients—translating WS-BD requests to and from biometric sensor commands.

Description: ___separated

Figure 2. A physically separated WS-Biometric Devices (WS-BD) implementation.

Figure 3 depicts a physically integrated service. In this scenario, a single hardware device has an embedded biometric sensor, as well as a web service. Analogous (but not identical) functionality is seen in many network printers; it is possible to point a web browser to a local network address, and obtain a web page that displays information about the state of the printer, such as toner and paper levels (WS-BD enabled devices do not provide web pages to a browser). Clients make requests directly to the integrated device; and a web service running within an embedded system translates the WS-BD requests to and from biometric sensor commands.

Description: __integrated

Figure 3. A physically integrated WS-Biometric Devices (WS-BD) implementation.

The “separated” versus “integrated” distinction is a simplification with a potential for ambiguity. For example, one might imagine putting a hardware shell around a USB fingerprint sensor connected to a small form-factor computer. Inside the shell, the sensor service and sensor are on different physical components. Outside the shell, the sensor service and sensor appear integrated. Logical encapsulations, i.e., layers of abstraction, can facilitate analogous “hiding”. The definition of what constitutes the “same” physical component depends on the particular implementation and the intended level of abstraction. Regardless, it is a useful distinction in that it illustrates the flexibility afforded by leveraging highly interoperable communications protocols. As suggested in §2.2.2 practitioners may need to clearly define appropriate logical and physical boundaries for their own context of use.

2.4 General Service Behavior

The following section describes the general behavior of WS-BD clients and services.

2.4.1 Security Model

In this version of the specification, it is assumed that if a client is able to establish a connection with the sensor service, then the client is fully authorized to use the service. This implies that all successfully connected clients have equivalent access to the same service. Clients might be required to connect through various HTTP protocols, such as HTTPS with client-side certificates, or a more sophisticated protocol such as Open Id (http://openid.net/) and/or OAuth.

Specific security measures are out of scope of this specification, but should be carefully considered when implementing a WS-BD service. Some recommended solutions to general scenarios are outlined Appendix D.

2.4.2 HTTP Request-Response Usage

Most biometrics devices are inherently single user—i.e., they are designed to sample the biometrics from a single user at a given time. Web services, on the other hand, are intended for stateless and multiuser use. A biometric device exposed via web services must therefore provide a mechanism to reconcile these competing viewpoints.

Notwithstanding the native limits of the underlying web server, WS-BD services must be capable of handling multiple, concurrent requests. Services must respond to requests for operations that do not require exclusive control of the biometric sensor and must do so without waiting until the biometric sensor is in a particular state.

Because there is no well-accepted mechanism for providing asynchronous notification via REST, each individual operation must block until completion. That is, the web server does not reply to an individual HTTP request until the operation that is triggered by that request is finished.

Individual clients are not expected to poll—rather they make a single HTTP request and block for the corresponding result. Because of this, it is expected that a client would perform WS-BD operations on an independent thread, so not to interfere with the general responsiveness of the client application. WS-BD clients therefore must be configured in such a manner such that individual HTTP operations have timeouts that are compatible with a particular implementation.

WS-BD operations may be longer than typical REST services. Consequently, there is a clear need to differentiate between service level errors and HTTP communication errors. WS-BD services must pass-through the status codes underlying a particular request. In other words, services must not use (or otherwise ‘piggyback’) HTTP status codes to indicate failures that occur within the service. If a service successfully receives a well-formed request, then the service must return the HTTP status code 200 indicating such. Failures are described within the contents of the XML data returned to the client for any given operation. The exception to this is when the service receives a poorly-formed request (i.e., the XML payload is not valid), then the service may return the HTTP status code 400, indicating a bad request.

This is deliberately different from REST services that override HTTP status codes to provide service-specific error messages. Avoiding the overloading of status codes is a pattern that facilitates the debugging and troubleshooting of communication versus client & service failures.

Design Note: Overriding HTTP status codes is just one example of the rich set of features afforded by HTTP; content negotiation, entity tags (e-tags), and preconditions are other features that could be leveraged instead of “recreated” (to some degree) within this specification. However, the authors avoided the use of these advanced HTTP features in this version of the specification for several reasons:

· To reduce the overall complexity required for implementation.

· To ease the requirements on clients and servers (particularly since the HTTP capabilities on embedded systems may be limited).

· To avoid dependencies on any HTTP feature that is not required (such as entity tags).

In summary, the goal for this initial version of the specification is to provide common functionality across the broadest set of platforms. As this standard evolves, the authors will continue to evaluate the integration of more advanced HTTP features, as well as welcome feedback on their use from users and/or implementers of the specification.

2.4.3 Client Identity

Before discussing how WS-BD balances single-user vs. multi-user needs, it is necessary to understand the WS-BD model for how an individual client can easily and consistently identify itself to a service.

HTTP is, by design, a stateless protocol. Therefore, any persistence about the originator of a sequence of requests must be built in (somewhat) artificially to the layer of abstraction above HTTP itself. This is accomplished in WS-BD via a session—a collection of operations that originate from the same logical endpoint. To initiate a session, a client performs a registration operation and obtains a session identifier (or “session id”). During subsequent operations, a client uses this identifier as a parameter to uniquely identify itself to a server. When the client is finished, it is expected to close a session with an unregistration operation. To conserve resources, services may automatically unregister clients that do not explicitly unregister after a period of inactivity (see §6.4.2.1).

This use of a session id directly implies that the particular sequences that constitute a session are entirely the responsibility of the client. A client might opt to create a single session for its entire lifetime, or, might open (and close) a session for a limited sequence of operations. WS-BD supports both scenarios.

It is possible, but discouraged, to implement a client with multiple sessions with the same service simultaneously. For simplicity, and unless otherwise stated, this specification is written in a manner that assumes that a single client maintains a single session id. (This can be assumed without loss of generality, since a client with multiple sessions to a service could be decomposed into “sub-clients”—one sub- client per session id.)

Just as a client might maintain multiple session ids, a single session id might be shared among a collection of clients. By sharing the session id, a biometric sensor may then be put in a particular state by one client, and then handed-off to another client. This specification does not provide guidance on how to perform multi-client collaboration. However, session id sharing is certainly permitted, and a deliberate artifact of the convention of using of the session id as the client identifier. Likewise, many-to-many relationships (i.e., multiple session ids being shared among multiple clients) are also possible, but should be avoided.

2.4.4 Sensor Identity

In general, implementers should map each target biometric sensor to a single endpoint (URI). However, just as it is possible for a client to communicate with multiple services, a host might be responsible for controlling multiple target biometric sensors.

Independent sensors should be exposed via different URIs.

Example: Figure 4 shows a physically separate implementation where a single host machine controls two biometric sensors—one fingerprint scanner and one digital camera. The devices act independently and are therefore exposed via two different services—one at the URL http://wsbd/fingerprint and one at http://wsbd/camera.

Figure 4. Independent sensors controlled by separate services

A service that controls multiple biometric devices simultaneously (e.g., an array of cameras with synchronized capture) should be exposed via the same endpoint.

Figure 5. A sensor array controlled by a single service

Example: Figure 5 shows a physically separate implementation where a single host machine controls a pair of cameras used for stereo vision. The cameras act together as a single logical sensor and are both exposed via the same service, http://wsbd/camera_array.

2.4.5 Locking

WS-BD uses a lock to satisfy two complementary requirements:

1. A service must have exclusive, sovereign control over biometric sensor hardware to perform a particular sensor operation such as initialization, configuration, or capture.

2. A client needs to perform an uninterrupted sequence of sensor operations.

Each WS-BD service exposes a single lock (one per service) that controls access to the sensor. Clients obtain the lock in order to perform a sequence of operations that should not be interrupted. Obtaining the lock is an indication to the server (and indirectly to peer clients) that (1) a series of sensor operations is about to be initiated and (2) that server may assume sovereign control of the biometric sensor.

A client releases the lock upon completion of its desired sequence of tasks. This indicates to the server (and indirectly to peer clients) that the uninterruptable sequence of operations is finished. A client might obtain and release the lock many times within the same session or a client might open and close a session for each pair of lock/unlock operations. This decision is entirely dependent on a particular client.

The statement that a client might “own” or “hold” a lock is a convenient simplification that makes it easier to understand the client-server interaction. In reality, each sensor service maintains a unique global variable that contains a session id. The originator of that session id can be thought of as the client that “holds” the lock to the service. Clients are expected to release the lock after completing their required sensor operations, but there is lock stealing—a mechanism for forcefully releasing locks. This feature is necessary to ensure that one client cannot hold a lock indefinitely, denying its peers access to the biometric sensor.

As stated previously (see §2.4.3), it is implied that all successfully connected clients enjoy the same access privileges. Each client is treated the same and are expected to work cooperatively with each other. This is critically important, because it is this implied equivalence of “trust” that affords a lock stealing operation.

Design Note: In the early development states of this specification, the authors considered having a single, atomic sensor operation that performed initialization, configuration and capture. This would avoid the need for locks entirely, since a client could then be ensured (if successful), the desired operation completed as requested. However, given the high degree of variability of sensor operations across different sensors and modalities, the explicit locking was selected so that clients could have a higher degree of control over a service and a more reliable way to predict timing. Regardless of the enforcement mechanism, it is undesirable if once a “well-behaved” client started an operation and a “rogue” client changed the internal state of the sensor midstream.

2.4.5.1 Pending Operations

Changing the state of the lock must have no effect on pending (i.e., currently running) sensor operations. That is, a client may unlock, steal, or even re-obtain the service lock even if the target biometric sensor is busy. When lock ownership is transferred during a sensor operation, overlapping sensor operations are prevented by sensor operations returning sensorBusy.

2.4.6 Operations Summary

All WS-BD operations fall into one of eight categories:

1. Registration

2. Locking

3. Information

4. Initialization

5. Configuration

6. Capture

7. Download

8. Cancellation

Of these, the initialization, configuration, capture, and cancellation operations are all sensor operations (i.e., they require exclusive sensor control) and require locking. Registration, locking, and download are all non-sensor operations. They do not require locking and (as stated earlier) must be available to clients regardless of the status of the biometric sensor.

Download is not a sensor operation as this allows for a collection of clients to dynamically share acquired biometric data. One client might perform the capture and hand off the download responsibility to a peer.

The following is a brief summary of each type of operation:

· Registration operations open and close (unregister) a session.

· Locking operations are used by a client to obtain the lock, release the lock, and steal the lock.

· Information operations query the service for information about the service itself, such as the supported biometric modalities, and service configuration parameters.

· The initialization operation prepares the biometric sensor for operation.

· Configuration operations get or set sensor parameters.

· The capture operation signals to the sensor to acquire a biometric.

· Download operations transfer the captured biometric data from the service to the client.

· Sensor operations can be stopped by the cancellation operation.

2.4.7 Idempotency

The W3C Web Services glossary [WSGloss] defines idempotency as:

[the] property of an interaction whose results and side-effects are the same whether it is done one or multiple times.

When regarding an operation’s idempotence, it should be assumed no other operations occur in between successive operations, and that each operation is successful. Notice that idempotent operations may have side-effects—but the final state of the service must be the same over multiple (uninterrupted) invocations.

The following example illustrates idempotency using an imaginary web service.

Example: A REST-based web service allows clients to create, read, update, and delete customer records from a database. A client executes an operation to update a customer’s address from “123 Main St” to “100 Broad Way.”

Suppose the operation is idempotent. Before the operation, the address is “123 Main St”. After one execution of the update, the server returns “success”, and the address is “100 Broad Way”. If the operation is executed a second time, the server again returns “success,” and the address remains “100 Broad Way”.

Now suppose that when the operation is executed a second time, instead of returning “success”, the server returns “no update made”, since the address was already “100 Broad Way.” Such an operation is not idempotent, because executing the operation a second time yielded a different result than the first execution.

The following is an example in the context of WS-BD.

Example: A service has an available lock. A client invokes the lock operation and obtains a “success” result. A subsequent invocation of the operation also returns a “success” result. The operation being idempotent means that the results (“success”) and side-effects (a locked service) of the two sequential operations are identical.

To best support robust communications, WS-BD is designed to offer idempotent services whenever possible.

2.4.8 Service Lifecycle Behavior

The lifecycle of a service (i.e., when the service starts responding to requests, stops, or is otherwise unavailable) must be modeled after an integrated implementation. This is because it is significantly easier for a physically separated implementation to emulate the behavior of a fully integrated implementation than it is the other way around. This requirement has a direct effect on the expected behavior of how a physically separated service would handle a change in the target biometric sensor.

Specifically, on a desktop computer, hot-swapping the target biometric sensor is possible through an operating system’s plug-and-play architecture. By design, this specification does not assume that it is possible to replace a biometric sensor within an integrated device. Therefore, having a physically separated implementation emulate an integrated implementation provides a simple means of providing a common level of functionality.

By virtue of the stateless nature of the HTTP protocol, a client has no simple means of detecting if a web service has been restarted. For most web communications, a client should not require this—it is a core capability that constitutes the robustness of the web. Between successive web requests, a web server might be restarted on its host any number of times. In the case of WS-BD, replacing an integrated device with another (configured to respond on the same endpoint) is an effective restart of the service. Therefore, by the emulation requirement, replacing the device within a physically separated implementation must behave similarly.

A client may not be directly affected by a service restart, if the service is written in a robust manner. For example, upon detecting a new target biometric sensor, a robust server could quiesce (refusing all new requests until any pending requests are completed) and automatically restart.

Upon restarting, services should return to a fully reset state—i.e., all sessions should be dropped, and the lock should not have an owner. However, a high-availability service may have a mechanism to preserve state across restarts, but is significantly more complex to implement (particularly when using integrated implementations!). A client that communicated with a service that was restarted would lose both its session and the service lock (if held). With the exception of the get service info operation, through various fault statuses a client would receive indirect notification of a service restart. If needed, a client could use the service’s common info timestamp (§A.1.1) to detect potential changes in the get service info operation.

3 Data Dictionary

This section contains descriptions of the data elements that are contained within the WS-BD data model. Each data type is described via an accompanying XML Schema type definition [XSDPart1, XSDPart2].

Refer to Appendix A for a complete XML schema containing all types defined in this specification.

3.1 Namespaces

The following namespaces, and corresponding namespace prefixes are used throughout this document.

Prefix	Namespace	Remarks
xs	http://www.w3.org/2001/XMLSchema	The xs namespace refers to the XML Schema specification. Definitions for the xs data types (i.e., those not explicitly defined here) can be found in [XSDPart2].
xsi	http://www.w3.org/2001/XMLSchema-instance	The xsi namespace allows the schema to refer to other XML schemas in a qualified way.
wsbd	http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0	The wsbd namespace is a uniform resource name [RFC1737, RFC2141] consisting of an object identifier [RFC3001] reserved for this specification’s schema. This namespace can be written in ASN.1 notation as {joint-iso-ccitt(2) country(16) us(840) organization(1) gov(101) csor(3) biometrics(9) wsbd(3) version1(1)}.

All of the datatypes defined in this section (§3) belong to the wsbd namespace defined in the above table. If a datatype is described in the document without a namespace prefix, the wsbd prefix is assumed.

3.2 UUID

A UUID is a unique identifier as defined in [RFC4122]. A service must use UUIDs that conform to the following XML Schema type definition.

<xs:simpleType name="UUID">

<xs:restriction base="xs:string">

<xs:pattern value="[\da-fA-F]{8}-[\da-fA-F]{4}-[\da-fA-F]{4}-[\da-fA-F]{4}-[\da-fA-F]{12}"/>

</xs:restriction>

</xs:simpleType>

Example: Each of the following code fragments contains a well-formed UUID. Enclosing tags (which may vary) are omitted.

E47991C3-CA4F-406A-8167-53121C0237BA

10fa0553-9b59-4D9e-bbcd-8D209e8d6818

161FdBf5-047F-456a-8373-D5A410aE4595

3.3 Dictionary

A Dictionary is a generic container used to hold an arbitrary collection of name-value pairs.

<xs:complexType name="Dictionary">

<xs:sequence>

<xs:element name="item" minOccurs="0" maxOccurs="unbounded">

<xs:complexType>

<xs:sequence>

<xs:element name="key" type="xs:string" nillable="true"/>

<xs:element name="value" type="xs:anyType" nillable="true"/>

</xs:sequence>

</xs:complexType>

</xs:element>

</xs:sequence>

</xs:complexType>

EXAMPLE: A query to get the metadata of a capture returns a dictionary of supported settings and the values at the time of capture. Enclosing tags (which may vary) are omitted.

<item>

<key>imageWidth</key>

</item>

<item>

<key>imageHeight</key>

</item>

<item>

<key>captureDate</key>

</item>

Dictionary instances are nestable—i.e., the value element of one Dictionary can contain another Dictionary. The use of xs:anyType allows for an XML element of any structure or definition to be used. Using types not defined in this document or types defined in W3’s XML Schema recommendations [XSDPart1, XSDPart2] might require a client to have unique knowledge about the service. Because the requirement of unique knowledge negatively impacts interoperability, using such elements is discouraged.

3.4 Parameter

A Parameter is a container used to describe the parameters or settings of a service or sensor.

<xs:complexType name="Parameter">

<xs:sequence>

<xs:element name="name" type="xs:string" nillable="true"/>

<xs:element name="type" type="xs:QName" nillable="true"/>

<xs:element name="readOnly" type="xs:boolean" minOccurs="0"/>

<xs:element name="supportsMultiple" type="xs:boolean" minOccurs="0"/>

<xs:element name="defaultValue" type="xs:anyType" nillable="true"/>

<xs:element name="allowedValues" nillable="true" minOccurs="0">

<xs:complexType>

<xs:sequence>

<xs:element name="allowedValue" type="xs:anyType" nillable="true" minOccurs="0" maxOccurs="unbounded"/>

</xs:sequence>

</xs:complexType>

</xs:element>

</xs:sequence>

</xs:complexType>

See §4 for more information on metadata and the use of Parameter.

3.4.1.1 Element Summary

The following is a brief informative description of each Parameter element.

Element	Description
name	The name of the parameter.
type	The fully qualified type of the parameter.
readOnly	Whether or not this parameter is read-only.
supportsMultiple	Whether or not this parameter can support multiple values for this parameter (§3.4.1.2).
defaultValue	The default value of this parameter.
allowedValues	A list of allowed values for this parameter (§3.4.1.3).

3.4.1.2 Supports Multiple

In some cases, a parameter might require multiple values. This flag specifies whether the parameter is capable of multiple values.

When supportsMultiple is true, communicating values must be done through a defined array type. If a type-specialized array is defined in this specification, such as a StringArray (§3.7) for xs:string, such type should be used. The generic Array (§3.6) type must be used in all other cases.

The parameter’s type element must be the qualified name of a single value. For example, if the parameter expects multiple strings during configuration, then the type must be xs:string and not StringArray.

Example: An iris scanner might have the ability to capture a left iris, right iris, and/or frontal face image simultaneously. This example configures the scanner to capture left and right iris images together. The first code block is what the service exposes to the clients. The second code block is how a client would configure this parameter. The client configures the submodality by supplying a StringArray with two elements: left and right—this tells the service to capture both the left and right iris. It is important to note that in this example, submodality exposes values for two modalities: iris and face. The resulting captured data must specify the respective modality for each captured item in its metadata. In both examples, enclosing tags (which may vary) are omitted.

<name>submodality</name>

<type>xs:string</type>

<readOnly>false</readOnly>

<element>leftIris</element>

<element>rightIris</element>

</defaultValue>

<allowedValue>leftIris</allowedValue>

<allowedValue>rightIris</allowedValue>

<allowedValue>frontalFace</allowedValue>

</allowedValues>

<item>

<key>submodality</key>

<element>leftIris</element>

<element>rightIris</element>

</value>

</item>

3.4.1.3 Allowed Values

For parameters that are not read-only and have restrictions on what values it may have, this allows the service to dynamically expose it to its clients.

Example: The following code block demonstrates a parameter, “CameraFlash”, with only three valid values. Enclosing tags (which may vary) are omitted.

<name>cameraFlash</name>

<type>xs:string</type>

<readOnly>false</readOnly>

<supportsMultiple>false</supportsMultiple>

</allowedValues>

Parameters requiring a range of values should be described by using Range (§3.5). Because the allowed type is not the same as its parameter type, a service must have logic to check for a Range and any appropriate validation.

Example: The following code block demonstrates a parameter, “CameraZoom”, where the allowed value is of type Range and consists of integers. Enclosing tags (which may vary) are omitted.

<name>cameraZoom</name>

<type>xs:integer</type>

<readOnly>false</readOnly>

<supportsMultiple>false</supportsMultiple>

</allowedValue>

</allowedValues>

Configurable parameters with no restrictions on its value must not include this element.

3.5 Range

A Range is a container used to describe a range of data, and whether the upper and lower bounds are exclusive. The upper and lower bounds must be inclusive by default.

<xs:complexType name="Range">

<xs:sequence>

<xs:element name="minimum" type="xs:anyType" nillable="true" minOccurs="0"/>

<xs:element name="maximum" type="xs:anyType" nillable="true" minOccurs="0"/>

<xs:element name="minimumIsExclusive" type="xs:boolean" nillable="true" minOccurs="0"/>

<xs:element name="maximumIsExclusive" type="xs:boolean" nillable="true" minOccurs="0"/>

</xs:sequence>

</xs:complexType>

Example: An example range of numbers from 0 to 100. The minimum is exclusive while the maximum is inclusive. Enclosing tags (which may vary) are omitted.

<maximumIsExclusive>false</maximumIsExclusive>

3.5.1.1 Element Summary

The following is a brief informative description of each Range element.

Element	Description
minimum	The lower bound of the range.
maximum	The upper bound of the range.
minimumIsExclusive	Boolean indicating whether the lower bound is exclusive or not. This is true by default.
maximumIsExclusive	Boolean indicating whether the upper bound is exclusive or not. This is true by default.

3.6 Array

An Array is a generic container used to hold a collection of elements.

<xs:complexType name="Array">

<xs:sequence>

<xs:element name="element" type="xs:anyType" nillable="true" minOccurs="0" maxOccurs="unbounded"/>

</xs:sequence>

</xs:complexType>

Example: Each of the following code fragments is an example of a valid Array. Enclosing tags (which may vary) are omitted.

<element>flatLeftThumb</element><element>flatRightThumb</element>

In this fragment (above), the values “flatLeftThumb” and “flatRightThumb” are of type xs:anyType, (and are likely to be deserialized as a generic “object.”

<element xsi:type="xs:boolean">false</element><element xsi:type="xs:int">1024</element>

Notice that in this fragment (above) the two values are of different types

In this fragment (above) the array contains a single element.

3.7 StringArray

A StringArray is a generic container used to hold a collection of strings.

<xs:complexType name="StringArray">

<xs:sequence>

<xs:element name="element" type="xs:string" nillable="true" minOccurs="0" maxOccurs="unbounded"/>

</xs:sequence>

</xs:complexType>

Example: Each of the following code fragments is an example of a valid StringArray. Enclosing tags (which may vary) are omitted.

<element>flatLeftThumb</element><element>flatRightThumb</element>

<element>value1</element><element>value2</element>

<element>sessionId</element>

3.8 UuidArray

A UuidArray is a generic container used to hold a collection of UUIDs.

<xs:complexType name="UuidArray">

<xs:sequence>

<xs:element name="element" type="wsbd:UUID" nillable="true" minOccurs="0" maxOccurs="unbounded"/>

</xs:sequence>

</xs:complexType>

Example: The following code fragment is an example of a single UuidArray with three elements. Enclosing tags (which may vary) are omitted.

3.9 ResourceArray

A ResourceArray is a generic container used to hold a collection of Resources (§3.10).

<xs:complexType name="ResourceArray">

<xs:sequence>

<xs:element name="element" type="wsbd:Resource" nillable="true" minOccurs="0" maxOccurs="unbounded"/>

</xs:sequence>

</xs:complexType>

EXAMPLE: The following code fragment is an example of a single ResourceArray with two elements. Enclosing tags (which may vary) are omitted.

<element><uri>file:///tmp/test.png<uri><contentType>image/png</contentType></element>

<element><uri>http://192.168.1.1/robots.txt<uri><contentType>text/plain</contentType></element>

3.10 Resource

Resource is a container to describe a resource at a specified URI.

<xs:complexType name="Resource">

<xs:sequence>

<xs:element name="uri" type="xs:anyURI"/>

<xs:element name="contentType" type="xs:string" nillable="true" minOccurs="0"/>

<xs:element name="relationship" type="xs:string" nillable="true" minOccurs="0"/>

</xs:sequence>

</xs:complexType>

3.11 Resolution

Resolution is a generic container to describe values for a width and height and optionally a description of the unit.

<xs:complexType name="Resolution">

<xs:sequence>

<xs:element name="width" type="xs:decimal"/>

<xs:element name="height" type="xs:decimal"/>

<xs:element name="unit" type="xs:string" nillable="true" minOccurs="0"/>

</xs:sequence>

</xs:complexType>

3.11.1.1 Element Summary

The following is a brief informative description of each Size element.

Element	Description
width	The decimal value of the width
height	The decimal value of the height
unit	A string describing the units of the width and height values

3.12 Status

The Status represents a common enumeration for communicating state information about a service.

<xs:simpleType name="Status">

<xs:restriction base="xs:string">

<xs:enumeration value="success"/>

<xs:enumeration value="failure"/>

<xs:enumeration value="invalidId"/>

<xs:enumeration value="canceled"/>

<xs:enumeration value="canceledWithSensorFailure"/>

<xs:enumeration value="sensorFailure"/>

<xs:enumeration value="lockNotHeld"/>

<xs:enumeration value="lockHeldByAnother"/>

<xs:enumeration value="initializationNeeded"/>

<xs:enumeration value="configurationNeeded"/>

<xs:enumeration value="sensorBusy"/>

<xs:enumeration value="sensorTimeout"/>

<xs:enumeration value="unsupported"/>

<xs:enumeration value="badValue"/>

<xs:enumeration value="noSuchParamter"/>

<xs:enumeration value="preparingDownload"/>

</xs:restriction>

</xs:simpleType>

3.12.1.1 Definitions

The following table defines all of the potential values for the Status enumeration.

Value	Description
success	The operation completed successfully.
failure	The operation failed. The failure was due to a web service (as opposed to a sensor error).
invalidId	The provided id is not valid. This can occur if the client provides a (session or capture) id that is either: unknown to the server (i.e., does not correspond to a known registration or capture result), or the session has been closed by the service (§6.4.2.1) (See §6.1.2 for information on parameter failures.)
canceled	The operation was canceled. NOTE: A sensor service may cancel its own operation, for example, if an operation is taking too long. This can happen if a service maintains its own internal timeout that is shorter than a sensor timeout.
canceledWithSensorFailure	The operation was canceled, but during (and perhaps because of) cancellation, a sensor failure occurred. This particular status accommodates for hardware that may not natively support cancellation.
sensorFailure	The operation could not be performed because of a biometric sensor (as opposed to web service) failure. Note: Clients that receive a status of sensorFailure should assume that the sensor will need to be reinitialized in order to restore normal operation.
lockNotHeld	The operation could not be performed because the client does not hold the lock. Note: This status implies that at the time the lock was queried, no other client currently held the lock. However, this is not a guarantee that any subsequent attempts to obtain the lock will succeed.
lockHeldByAnother	The operation could not be performed because another client currently holds the lock.
initializationNeeded	The operation could not be performed because the sensor requires initialization.
configurationNeeded	The operation could not be performed because the sensor requires configuration.
sensorBusy	The operation could not be performed because the sensor is currently performing another task. Note: Services may self-initiate an activity that triggers a sensorBusy result. That is, it may not be possible for a client to trace back a sensorBusy status to any particular operation. An automated self-check, heartbeat, or other activity such as a data transfer may place the target biometric sensor into a “busy” mode. (See §6.13.2.2 for information about post-acquisition processing.)
sensorTimeout	The operation was not performed because the biometric sensor experienced a timeout. Note: The most common cause of a sensor timeout would be a lack of interaction with a sensor within an expected timeframe.
unsupported	The service does not support the requested operation. (See §6.1.2 for information on parameter failures.)
badValue	The operation could not be performed because a value provided for a particular parameter was either (a) an incompatible type or (b) outside of an acceptable range. (See §6.1.2 for information on parameter failures.)
noSuchParameter	The operation could not be performed because the service did not recognize the name of a provided parameter. (See §6.1.2 for information on parameter failures.)
preparingDownload	The operation could not be performed because the service is currently preparing captured data for download. (See §6.13.2.2)

Many of the permitted status values have been designed specifically to support physically separate implementations—a scenario where it is easier to distinguish between failures in the web service and failures in the biometric sensor. This is not to say that within an integrated implementation such a distinction is not possible, only that some of the status values are more relevant for physically separate versions.

For example, a robust service would allow all sensor operations to be canceled with no threat of a failure. Unfortunately, not all commercial, off-the-shelf (COTS) sensors natively support cancellation. Therefore, the canceledWithSensorFailure status is offered to accommodate this. Implementers can still offer cancellation, but have a mechanism to communicate back to the client that sensor initialization might be required.

3.13 Result

Unless a service returns with an HTTP error, all WS-BD operations must reply with an HTTP message that contains an element of a Result type that conforms to the following XML Schema snippet.

<xs:element name="result" type="wsbd:Result" nillable="true"/>

<xs:complexType name="Result">

<xs:sequence>

<xs:element name="status" type="wsbd:Status"/>

<xs:element name="badFields" type="wsbd:StringArray" nillable="true" minOccurs="0"/>

<xs:element name="captureIds" type="wsbd:UuidArray" nillable="true" minOccurs="0"/>

<xs:element name="metadata" type="wsbd:Dictionary" nillable="true" minOccurs="0"/>

<xs:element name="message" type="xs:string" nillable="true" minOccurs="0"/>

<xs:element name="sensorData" type="xs:base64Binary" nillable="true" minOccurs="0"/>

<xs:element name="sessionId" type="wsbd:UUID" nillable="true" minOccurs="0"/>

</xs:sequence>

</xs:complexType>

3.13.1 Terminology Shorthand

Since a Result is the intended outcome of all requests, this document may state that an operation “returns” a particular status value. This is shorthand for a Result output payload with a status element containing that value.

Example: The following result payload “returns success”. A result might contain other child elements depending on the specific operation and result status—see §5 for operations and their respective details.

<result xmlns="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0"

xmlns:xs="http://www.w3.org/2001/XMLSchema"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<status>success</status>

</result>

Likewise, the same shorthand is implied by a client “receiving” a status, or an operation “yielding” a status.

3.13.2 Required Elements

Notice that from a XML Schema validation perspective [XSDPart1], a schema-valid Result must contain a status element, and may contain any of the remaining elements.

The specific permitted elements of a Result are determined via a combination of (a) the operation, and (b) the result’s status. That is, different operations will have different requirements on which elements are permitted or forbidden, depending on that operation’s status.

Example: As will be detailed later (§6.3.4.1 and §6.5.4.1), a register operation returning a status of success must also populate the sessionId element. However, a try lock operation that returns a status of success cannot populate any element other than status.

Design note: An XML inheritance hierarchy could have been used to help enforce which elements are permitted under which circumstances. However, a de-normalized representation (in which all of the possible elements are valid with respect to a schema) was used to simplify client and server implementation. Further, this reduces the burden of managing an object hierarchy for the sake of enforcing simple constraints.

3.13.3 Element Summary

The following is a brief informative description of each Result element.

Element	Description
status	The disposition of the operation. All Result elements must contain a status element. (Used in all operations.)
badFields	The list of fields that contain invalid or ill-formed values. (Used in almost all operations.)
captureIds	Identifiers that may be used to obtain data acquired from a capture operation (§6.12, §6.13).
metadata	This field may hold a) metadata for the service (§6.8), or b) a service and sensor’s configuration (§6.10, §6.11), or c) metadata relating to a particular capture (§6.13, §6.14, §6.15) (See §4for more information regarding metadata)
message	A string providing informative detail regarding the output of an operation. (Used in almost all operations.)
sensorData	The biometric data corresponding to a particular capture identifier (§6.13, §6.15).
sessionId	A unique session identifier (§6.3).

3.14 Validation

The provided XML schemas may be used for initial XML validation. It should be noted that these are not strict schema definitions and were designed for easy consumption of web service/code generation tools. Additional logic should be used to evaluate the contents and validity of the data where the schema falls short. For example, additional logic will be necessary to verify the contents of a Result are accurate as there is not a different schema definition for every combination of optional and mandatory fields.

A service must have separate logic validating parameters and their values during configuration. The type of any allowed values might not correspond with the type of the parameter. For example, if the type of the parameter is an integer and an allowed value is a Range, the service must handle this within the service as it cannot be appropriately validated using XML schema.

4 Metadata

Metadata can be broken down into three smaller categories: service information, sensor information or configuration, and capture information. Metadata can be returned in two forms: as a key/value pair within a Dictionary or a Dictionary of Parameter types.

4.1 Service Information

Service information includes read-only parameters unrelated to the sensor as well as parameters that can be set. Updating the values of a parameter should be done in the set configuration operation.

Service information must include the required parameters listed in Appendix A; including the optional parameters is highly recommended. Each parameter must be exposed as a Parameter (§3.4).

Parameters listed in §A.1, §A.2, and §A.3 must be exposed as read-only parameters.

Read-only parameters must specify its current value by populating the default value field with the value. Additionally, read-only parameters must not provide any allowed values. Allowed values are reserved to specify acceptable information which may be passed to the service for configuration.

Example: An example snippet from a get service info call demonstrating a read-only parameter. Enclosing tags (which may vary) are omitted.

<name>inactivityTimeout</name>

<type>xs:nonNegativeInteger</type>

<supportsMultiple>false</supportsMultiple>

Configurable parameters, or those which are not read only, must provide information for the default value as well as allowed values. To specify that an allowed value is within range of numbers, refer to Range (§3.5).

Example: An example snippet from a get service info call. The target service supports a configurable parameter called “ImageWidth”. Enclosing tags (which may vary) are omitted.

<name>imageWidth</name>

<type>xs:positiveInteger</type>

<readOnly>false</readOnly>

<supportsMultiple>false</supportsMultiple>

</allowedValues>

In many cases, an exposed parameter will support multiple values (see §3.4.1.2). When a parameter allows this capability, it must use a type-specific array, if defined in this specification, or the generic Array (§3.6) type. The type element within a parameter must be the qualified name of a single value’s type (see §3.4.1.2 for an example).

4.2 Configuration

A configuration consists of parameters specific to the sensor or post-processing related to the final capture result. This must only consist of key/value pairs. It must not include other information about the parameters, such as allowed values or read-only status.

Restrictions for each configuration parameter can be discovered through the get service info operation.

Example: The following is an example payload to set configuration consisting of three parameters.

<configuration xmlns="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0"

xmlns:xs="http://www.w3.org/2001/XMLSchema"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<item>

<key>imageHeight</key>

</item>

<item>

<key>imageWidth</key>

</item>

<item>

<key>frameRate</key>

</item>

</configuration>

4.3 Captured Data

Metadata related to a particular capture operation must include the configuration of the sensor at the time of capture. Static parameters related to the service should not be included in the metadata for a capture result.

A service may perform post-processing steps on any captured information. This information should be added to the particular capture result’s metadata.

Example: Example metadata for a particular capture. Note that this includes parameters related to the sensor. Enclosing tags (which may vary) are omitted.

<item>

<key>serialNumber</key>

</item>

<item>

<key>imageHeight</key>

</item>

<item>

<key>imageWidth</key>

</item>

<item>

<key>captureTime</key>

</item>

<item>

<key>contentType</key>

<value xsi:type="xs:string">image/jpeg</value>

</item>

<item>

<key>modality</key>

<value xsi:type="xs:string">Finger</value>

</item>

<item>

<key>submodality</key>

<value xsi:type="xs:string">LeftIndex</value>

</item>

Example: A service computes the quality score of a captured fingerprint (see previous example). This score is added to the result’s metadata to allow other clients to take advantage of previously completed processes. Enclosing tags (which may vary) are omitted.

<item>

<key>quality</key>

</item>

<item>

<key>serialNumber</key>

</item>

<item>

<key>captureDate</key>

</item>

<item>

<key>modality</key>

<value>Finger</value>

</item>

<item>

<key>submodality</key>

<value>leftIndex</value>

</item>

<item>

<key>imageHeight</key>

</item>

<item>

<key>imageWidth</key>

</item>

<item>

<key>contentType</key>

<value>image/bmp</value>

</item>

4.3.1 Minimal Metadata

At a minimum, a sensor or service must maintain the following metadata fields for each captured result.

4.3.1.1 Capture Date

Formal Name	captureDate
Data Type	xs:dateTime [XSDPart2]

This value represents the date and time at which the capture occurred.

4.3.1.2 Modality

Formal Name	modality
Data Type	xs:string [XSDPart2]

The value of this field must be present in the list of available modalities exposed by the get service info operation (§6.8) as defined in §A.4.1. This value represents the modality of the captured result.

4.3.1.3 Submodality

Formal Name	submodality
Data Type	xs:anyType [XSDPart2]

The value of this field must be present in the list of available submodalities exposed by the get service info operation (§6.8) as defined in §A.4.2. This value represents the submodality of the captured result. If this parameter supports multiple, then the data type must be a StringArray (§3.7) of values. If submodality does not support multiple, the data type must be xs:string [XSDPart2].

4.3.1.4 Content Type

Formal Name	contentType
Data Type	xs:string [RFC2045, RFC2046]

The value of this field represents the content type of the captured data. See Appendix B for which content types are supported.

5 Live Preview

The ability to provide live preview of a session provides feedback to the client on when to signal a capture and/or what is going on during a capture.

5.1 Endpoints

Exposing endpoint information to a client is done through the service information. If live preview is implemented, a key/value pair shall be added where the key is “livePreview” and the value is of type Parameter (§3.4). This must be a read-only parameter. The default value shall be of type ResourceArray (§3.9). An implementation may expose one or more Resources (§3.10) in the ResourceArray. For the stream parameter, each instance of a Resource shall contain the uri, contentType, and the relationship elements. The content type of the stream and the value of each Resource’s contentType element should be listed in Appendix B. The value of the relationship field must begin with “livePreview” and there must be at least one entry where the element’s value consists of only “livePreview”. An implementer may provide additional endpoints with a modified relationship. This may be done by appending a forward slash immediately after “livePreview” and before any additional content; any additional content must not occur before the forward slash. Only base-64 characters are allowed in the relationship field.

The follow snippet is a skeleton service information entry for a stream parameter. Enclosing tags have been omitted.

<item>

<key>livePreview</key>

<name>livePreview </name>

<type>Resource</type>

...

</defaultValue>

</value>

</item>

Example: The following snippet is an example service information entry that exposes a Parameter (§3.4) for live preview resources. This example exposes two different endpoints, each offering a live preview with different content types. Enclosing tags (which may vary) are omitted.

<item>

<key>livePreview</key>

<name>livePreview</name>

<type>Resource</type>

<uri>http://192.168.1.1/stream</uri>

<contentType>video/h264</contentType>

<relationship>livePreview</relationship>

</element>

<uri>http://192.168.1.1:81/stream</uri>

<contentType>video/mpeg</contentType>

<relationship>livePreview</relationship>

</element>

</defaultValue>

</value>

</item>

Example: The following snippet is an example service information entry that exposes a Parameter (§3.4) for live preview resources. This example exposes two different endpoints, one with a modified relationship value. For example, the second entry may be describing an endpoint that has live preview of a face at 30 frames per second. Enclosing tags (which may vary) are omitted.

<item>

<key>livePreview</key>

<name>livePreview</name>

<type>Resource</type>

<uri>http://192.168.1.1/stream</uri>

<contentType>video/h264</contentType>

<relationship>livePreview</relationship>

</element>

<uri>http://192.168.1.1:81/stream</uri>

<contentType>video/mpeg</contentType>

<relationship>livePreview/face+fps=30</relationship>

</element>

</defaultValue>

</value>

</item>

5.2 Heartbeat

In many cases, live preview may not be ready to provide actual images until a certain point in a session or the lifetime of a service (e.g., after initialization). The service has two options on how to proceed when streaming is called before it is ready.

Immediately close the live preview connection. This is only recommended if live preview is not available for the service. It shall not be expected that a client will make additional calls to the live preview endpoint after a closed connection.
Send a heartbeat to the client upon a live preview request. The heartbeat shall consist of minimal null information and shall be sent to all clients on a fixed time interval.

Example: The follow is an example heartbeat frame sent over a multipart/x-mixed-replace stream. For this example, the boundary indicator is boundaryString. A service may send this null frame as a heartbeat to all connected clients every, for example, 10 seconds to alert the client that live preview data is available, but not at the current state of the service, sensor, or session.

--boundaryString

Content-Type: multipart/x-heartbeat

--boundaryString

6 Operations

This section provides detailed information regarding each WS-BD operation.

6.1 General Usage Notes

The following usage notes apply to all operations, unless the detailed documentation for a particular operation conflicts with these general notes, in which case the detailed documentation takes precedence.

1. Failure messages are informative. If an operation fails, then the message element may contain an informative message regarding the nature of that failure. The message is for informational purposes only—the functionality of a client must not depend on the contents of the message.

2. Results must only contain required and optional elements. Services must only return elements that are either required or optional. All other elements must not be contained in the result, even if they are empty elements. Likewise, to maintain robustness in the face of a non-conformant service, clients should ignore any element that is not in the list of permitted Result elements for a particular operation call.

3. Sensor operations must not occur within a non-sensor operation. Services should only perform any sensor control within the operations:

a. initialize,

b. get configuration,

c. set configuration,

d. capture, and

e. cancel.

4. Sensor operations must require locking. Even if a service implements a sensor operation without controlling the target biometric sensor, the service must require that a locked service for the operation to be performed.

5. Content Type. Clients must make HTTP requests using a content type of application/xml [RFC2616, §14].

6. Namespace. A data type without an explicit namespace or namespace prefix implies it is a member of the wsbd namespace as defined in §3.1.

6.1.1 Precedence of Status Enumerations

To maximize the amount of information given to a client when an error is obtained, and to prevent different implementations from exhibiting different behaviors, all WS-BD services must return status values according to a fixed priority. In other words, when multiple status messages might apply, a higher-priority status must always be returned in favor of a lower-priority status.

The status priority, listed from highest priority (“invalidId”) to lowest priority (“success”) is as follows:

1. invalidId

2. noSuchParameter

3. badValue

4. unsupported

5. canceledWithSensorFailure

6. canceled

7. lockHeldByAnother

8. lockNotHeld

9. sensorBusy

10. sensorFailure

11. sensorTimeout

12. initializationNeeded

13. configurationNeeded

14. preparingDownload

15. failure

16. success

Notice that success is the lowest priority—an operation should only be deemed successful if no other kinds of (non-successful) statuses apply.

The following example illustrates how this ordering affects the status returned in a situation in which multiple clients are performing operations.

EXAMPLE: Figure 6 illustrates that client cannot receive a “sensorBusy” status if it does not hold the lock, even if a sensor operation is in progress (recall from §2.4.5 that sensor operations require holding the lock). Suppose there are two clients; Client A and Client B. Client A holds the lock and starts initialization on (Step 1–3). Immediately after Client A initiates capture, Client B (Step 4) tries to obtain the lock while Client A is still capturing. In this situation, the valid statuses that could be returned to Client B are “sensorBusy” (since the sensor is busy performing a capture) and “lockHeldByAnother” (since Client A holds the lock). In this case, the service returns “lockHeldByAnother” (Step 5) since “lockHeldByAnother” is higher priority than “sensorBusy.”

Figure 6. Example illustrating how a client cannot receive a "sensorBusy" status if it does not hold the lock.

6.1.2 Parameter Failures

Services must distinguish among badValue, invalidId, noSuchParameter, and unsupported according to the following rules. These rules are presented here in the order of precedence that matches the previous subsection.

1. Is a recognizable UUID provided? If the operation requires a UUID as an input URL parameter, and provided value is not an UUID (i.e., the UUID is not parseable), then the service must return badValue. Additionally, the Result’s badFields list must contain the name of the offending parameter (sessionId or captureId).

…otherwise…

2. Is the UUID understood? If an operation requires an UUID as an input URL parameter, and the provided value is a UUID, but service cannot accept the provided value, then the service must return invalidId. Additionally, the Result’s badFields list must contain the name of the offending parameter (sessionId or captureId).

…otherwise…

3. Are the parameter names understood? If an operation does not recognize a provided input parameter name, then the service must return noSuchParameter. This behavior may differ from service to service, as different services may recognize (or not recognize) different parameters. The unrecognized parameter(s) must be listed in the Result’s badFields list.

…otherwise…

4. Are the parameter values acceptable? If an operation recognizes all of the provided parameter names, but cannot accept a provided value because it is (a) and inappropriate type, or (b) outside the range advertised by the service (§4.1), the then service must return badValue. The parameter names associated with the unacceptable values must be listed in the Result’s badFields list. Clients are expected to recover the bad values themselves by reconciling the Result corresponding to the offending request.

…otherwise…

5. Is the request supported? If an operation accepts the parameter names and values, but the particular request is not supported by the service or the target biometric sensor, then the service must return unsupported. The parameter names that triggered this determination must be listed in the Result’s badFields list. By returning multiple fields, a service is able to imply that a particular combination of provided values is unsupported.

NOTE: It may be helpful to think of invalidId as a special case of badValue reserved for URL parameters of type UUID.

6.1.3 Visual Summaries

The following two tables provide informative visual summaries of WS-BD operations. These visual summaries are an overview; they are not authoritative. (§6.3–6.16 are authoritative.)

6.1.3.1 Input & Output

The following table represents a visual summary of the inputs and outputs corresponding to each operation.

Operation inputs are indicated in the “URL Fragment” and “Input Payload” columns. Operation inputs take the form of either (a) a URL parameter, with the parameter name shown in “curly brackets” (“{“ and “}”) within the URL fragment (first column), and/or, (b) a input payload (defined in §1.1).

Operation outputs are provided via Result, which is contained in the body of an operation’s HTTP response.

Summary of Operations Input/Output

Operation

URL Fragment

(Includes inputs)

Method

Input

payload

Idempotent

Sensor Operation

Permitted Result Elements
(within output payload)

Detailed Documentation (§)

status

badFields

sessionId

metadata

captureIds

sensorData

/register

POST

none

6.3

unregister

/register/{sessionId}

DELETE

none

6.4

try lock

/lock/{sessionId}

POST

none

6.5

steal lock

PUT

none

6.6

unlock

DELETE

none

6.7

get service info

/info

GET

none

6.8

initialize

/initialize/{sessionId}

POST

none

6.9

get configuration

/configure/{sessionId}

GET

none

6.10

set configuration

POST

config

6.11

capture

/capture/{sessionId}

POST

none

6.12

download

/download/{captureid}

GET

none

6.13

get download info

/download/{captureid}/info

GET

none

6.14

thrifty download

/download/{captureid}/{maxSize}

GET

none

6.15

cancel operation

/cancel/{sessionId}

POST

none

6.16

Presence of a symbol in a table cell indicates that operation is idempotent (u), a sensor operation (n), and which elements may be present in the operation's Result (l). Likewise, the lack of a symbol in a table cell indicates the operation is not idempotent, not a sensor operation, and which elements of the operation's Result are forbidden.

Example: The capture operation (fifth row from the bottom) is not idempotent, but is a sensor operation. The output may contain the elements status, badFields, and/or captureIds in its Result. The detailed information regarding the Result for capture, (i.e., which elements are specifically permitted under what circumstances) is found in §6.12.

The message element is not shown in this table for two reasons. First, when it appears, it is always optional. Second, to emphasize that the message content must only be used for informative purposes; it must not be used as a vehicle for providing unique information that would inhibit a service’s interoperability.

6.1.3.2 Permitted Status Values

The following table provides a visual summary of the status values permitted.

Possible Status Values Per Operation

Status

Values

Operation
Description

success

failure

invalidId

canceled

canceledWithSensorFailure

sensorFailure

lockNotHeld

lockHeldByAnother

initializationNeeded

configurationNeeded

sensorBusy

sensorTimeout

unsupported

badValue

noSuchParameter

preparingDownload

unregister

try lock

steal lock

unlock

get service info

initialize

get configuration

set configuration

capture

download

get download info

thrifty download

cancel

The presence (absence) of a symbol in a cell indicates that the respective status may (may not) be returned by the corresponding operation.

Example: The register operation may only return a Result with a Status that contains either success or failure. The unregister operation may only return success, failure, invalidId, sensorBusy, or badValue.

The visual summary does not imply that services may return these values arbitrarily—the services must adhere to the behaviors as specified in their respective sections.

6.2 Documentation Conventions

Each WS-BD operation is documented according to the following conventions.

6.2.1 General Information

Each operation begins with the following tabular summary:

Description	A short description of the operation
URL Template	The suffix used to access the operation. These take the form /resourceName or /resourceName/{URL_parameter_1}/…/{URL_parameter_N} Each parameter, {URL_parameter...} must be replaced, in-line with that parameter’s value. Parameters have no explicit names, other than defined by this document or reported back to the client within the contents of a badFields element. It is assumed that consumers of the service will prepend the URL to the service endpoint as appropriate. Example: The resource resourceName hosted at the endpoint http://example.com/Service would be accessible via http://example.com/Service/resourceName
HTTP Method	The HTTP method that triggers the operation, i.e., GET, POST, PUT, or DELETE
URL Parameters	A description of the URL-embedded operation parameters. For each parameter the following details are provided: · the name of the parameter · the expected data type (§3) · a description of the parameter
Input Payload	A description of the content, if any, to be posted to the service as input to an operation.
Idempotent	Yes—the operation is idempotent (§2.4.7). No—the operation is not idempotent.
Sensor Operation (Lock Required)	Yes—the service may require exclusive control over the target biometric sensor. No—this operation does not require a lock. Given the concurrency model (§2.4.5) this value doubles as documentation as to whether or not a lock is required

6.2.2 Result Summary

This subsection summarizes the various forms of a Result that may be returned by the operation. Each row represents a distinct combination of permitted values & elements associated with a particular status. An operation that returns success may also provide additional information other than status.

success	status="success"
failure	status="failure" message*=informative message describing failure
[status value]	status=status literal [required element name]=description of permitted contents of the element [optional element name]*=description of permitted contents of the element
…	…

For each row, the left column contains a permitted status value, and the right column contains a summary of the constraints on the Result when the status element takes that specific value. The vertical ellipses at the bottom of the table signify that the summary table may have additional rows that summarize other permitted status values.

Data types without an explicit namespace or namespace prefix are members of the wsbd namespace as defined in §3.1.

Element names suffixed with a ‘*’ indicate that the element is optional.

6.2.3 Usage Notes

Each of the following subsections describes behaviors & requirements that are specific to its respective operation.

6.2.4 Unique Knowledge

For each operation, there is a brief description of whether or not the operation affords an opportunity for the server or client to exchange information unique to a particular implementation. The term “unique knowledge” is used to reflect the definition of interoperability referenced in §2.1.

6.2.5 Return Values Detail

This subsection details the various return values that the operation may return. For each permitted status value, the following table details the Result requirements:

Status Value	The particular status value
Condition	The service accepts the registration request
Required Elements	A list of the required elements. For each required element, the element name, its expected contents, and expected data type is listed If no namespace prefix is specified, then the wsbd namespace (§3.1) is inferred. For example, badFields={"sessionId"} (StringArray, §3.7) Indicates that badFields is a required element, and that the contents of the element must be a wsbd:StringArray containing the single literal "sessionId".
Optional Elements	A list of the required elements. Listed for each optional element are the element names and its expected contents.

Constraints and information unique to the particular operation/status combination may follow the table, but some status values have no trailing explanatory text.

A data type without an explicit namespace or namespace prefix implies it is a member of the wsbd namespace as defined in §3.1.

6.3 Register

Description	Open a new client-server session
URL Template	/register
HTTP Method	POST
URL Parameters	None
Input Payload	None
Idempotent	No
Sensor Operation	No

6.3.1 Result Summary

success

status="success"

sessionId=session id (UUID, §3.2)

failure

status="failure"

message*=informative message describing failure

6.3.2 Usage Notes

In a sequence of operations with a service, a register operation is likely one of the first operations performed by a client (get service info being the other). It is expected (but not required) that a client would perform a single registration during that client’s lifetime.

Design Note: By using an UUID, as opposed to the source IP address, a server can distinguish among clients sharing the same originating IP address (i.e., multiple clients on a single machine, or multiple machines behind a firewall). Additionally, a UUID allows a client (or collection of clients) to determine client identity rather than enforcing a particular model (§2.4.3).

6.3.3 Unique Knowledge

As specified, the register operation cannot be used to provide or obtain knowledge about unique characteristics of a client or service.

6.3.4 Return Values Detail

The register operation must return a Result according to the following constraints.

6.3.4.1 Success

Status Value	success
Condition	The service accepts the registration request
Required Elements	status (Status, §3.12) the literal “success” sessionId (UUID, §3.2) an identifier that can be used to identify a session
Optional Elements	None

The “register” operation must not provide a sessionId of 00000000-0000-0000-0000-000000000000.

6.3.4.2 Failure

Status Value	failure
Condition	The service cannot accept the registration request
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

Registration might fail if there are too many sessions already registered with a service. The message element must only be used for informational purposes. Clients must not depend on particular contents of the message element to control client behavior.

See §4 and §A.1 for how a client can use sensor metadata to determine the maximum number of current sessions a service can support.

6.4 Unregister

Description	Close a client-server session
URL Template	/register/{sessionId}
HTTP Method	DELETE
URL Parameters	{sessionId} (UUID, §3.2) Identity of the session to remove
Input Payload	None
Idempotent	Yes
Sensor Operation	No

6.4.1 Result Summary

success	status="success"
failure	status="failure" message*=informative message describing failure
sensorBusy	status="sensorBusy"
badValue	status="badValue" badFields={"sessionId"} (StringArray, §3.7)

6.4.2 Usage Notes

Unregister closes a client-server session. Although not strictly necessary, clients should unregister from a service when it is no longer needed. Given the lightweight nature of sessions, services should support (on the order of) thousands of concurrent sessions, but this cannot be guaranteed, particularly if the service is running within limited computational resources. Conversely, clients should assume that the number of concurrent sessions that a service can support is limited. (See §A.1 for details on connection metadata.)

6.4.2.1 Inactivity

A service may automatically unregister a client after a period of inactivity, or if demand on the service requires that least-recently used sessions be dropped. This is manifested by a client receiving a status of invalidId without a corresponding unregistration. Services should set the inactivity timeout to a value specified in minutes. (See §A.1 for details on connection metadata.)

6.4.2.2 Sharing Session Ids

A session id is not a secret, but clients that share session ids run the risk of having their session prematurely terminated by a rogue peer client. This behavior is permitted, but discouraged. See §2.4 for more information about client identity and the assumed security models.

6.4.2.3 Locks & Pending Sensor Operations

If a client that holds the service lock unregisters, then a service must also release the service lock, with one exception. If the unregistering client both holds the lock and is responsible for a pending sensor operation, the service must return sensorBusy (See §6.4.4.3).

6.4.3 Unique Knowledge

As specified, the unregister operation cannot be used to provide or obtain knowledge about unique characteristics of a client or service.

6.4.4 Return Values Detail

The unregister operation must return a Result according to the following constraints.

6.4.4.1 Success

Status Value	success
Condition	The service accepted the unregistration request
Required Elements	status (Status, §3.12) the literal “success”
Optional Elements	None

If the unregistering client currently holds the service lock, and the requesting client is not responsible for any pending sensor operation, then successful unregistration must also release the service lock.

As a consequence of idempotency, a session id does not need to ever have been registered successfully in order to unregister successfully. Consequently, the unregister operation cannot return a status of invalidId.

6.4.4.2 Failure

Status Value	failure
Condition	The service could not unregister the session.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

In practice, failure to unregister is expected to be a rare occurrence. Failure to unregister might occur if the service experiences a fault with an external system (such as a centralized database used to track session registration and unregistration)

6.4.4.3 Sensor Busy

Status Value	sensorBusy
Condition	The service could not unregister the session because the biometric sensor is currently performing a sensor operation within the session being unregistered.
Required Elements	status (Status, §3.12) the literal “sensorBusy”
Optional Elements	None

This status must only be returned if (a) the sensor is busy and (b) the client making the request holds the lock (i.e., the session id provided matches that associated with the current service lock). Any client that does not hold the session lock must not result in a sensorBusy status.

Example: The following sequence diagram illustrates a client that cannot unregister (Client A) and a client that can unregister (Client B). After the initialize operation completes (Step 6), Client A can unregister (Steps 7-8).

Figure 7. Example of how an unregister operation can result in sensorBusy.

6.4.4.4 Bad Value

Status Value	badValue
Condition	The provided session id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.5 Try Lock

Description	Try to obtain the service lock
URL Template	/lock/{sessionId}
HTTP Method	POST
URL Parameters	{sessionId} (UUID, §3.2) Identity of the session requesting the service lock
Input Payload	None
Idempotent	Yes
Sensor Operation	No

6.5.1 Result Summary

success	status="success"
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId" badFields={"sessionId"} (StringArray, §3.7)
lockHeldByAnother	status="lockHeldByAnother"
badValue	status="badValue" badFields={"sessionId"} (StringArray, §3.7)

6.5.2 Usage Notes

The try lock operation attempts to obtain the service lock. The word “try” is used to indicate that the call always returns immediately; it does not block until the lock is obtained. See §2.4.5 for detailed information about the WS-BD concurrency and locking model.

6.5.3 Unique Knowledge

As specified, the try lock cannot be used to provide or obtain knowledge about unique characteristics of a client or service.

6.5.4 Return Values Detail

The try lock operation must return a Result according to the following constraints.

6.5.4.1 Success

Status Value	success
Condition	The service was successfully locked to the provided session id.
Required Elements	status (Status, §3.12) the literal “success”
Optional Elements	None

Clients that hold the service lock are permitted to perform sensor operations (§2.4.5). By idempotency (§2.4.7), if a client already holds the lock, subsequent try lock operations shall also return success.

6.5.4.2 Failure

Status Value	failure
Condition	The service could not be locked to the provided session id.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

Services must reserve a failure status to report system or internal failures and prevent the acquisition of the lock. Most try lock operations that do not succeed will not produce a failure status, but more likely a lockHeldByAnother status (See §6.5.4.4 for an example).

6.5.4.3 Invalid Id

Status Value	invalidId
Condition	The provided session id is not registered with the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

A session id is invalid if it does not correspond to an active registration. A session id may become unregistered from a service through explicit unregistration or triggered automatically by the service due to inactivity (§6.4.4.1).

See §6.1.2 for general information on how services must handle parameter failures.

6.5.4.4 Lock Held by Another

Status Value	lockHeldByAnother
Condition	The service could not be locked to the provided session id because the lock is held by another client.
Required Elements	status (Status, §3.12) the literal “lockHeldByAnother”
Optional Elements	None

Example: The following sequence diagram illustrates a client that cannot obtain the lock (Client B) because it is held by another client (Client A).

Figure 8. Example of a scenario yielding a lockHeldByAnother result.

6.5.4.5 Bad Value

Status Value	badValue
Condition	The provided session id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.6 Steal Lock

Description	Forcibly obtain the lock away from a peer client
URL Template	/lock/{sessionId}
HTTP Method	PUT
URL Parameters	{sessionId} (UUID, §3.2) Identity of the session requesting the service lock
Input Payload	None
Idempotent	Yes
Sensor Operation	No

6.6.1 Result Summary

success	status="success"
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId" badFields={"sessionId"} (StringArray, §3.7)
badValue	status="badValue" badFields={"sessionId"} (StringArray, §3.7)

6.6.2 Usage Notes

The steal lock operation allows a client to forcibly obtain the lock away from another client that already holds the lock. The purpose of this operation is to prevent a client that experiences a fatal error from forever preventing another client access to the service, and therefore, the biometric sensor.

6.6.2.1 Avoid Lock Stealing

Developers and integrators should endeavor to reserve lock stealing for exceptional circumstances—such as when a fatal error prevents a client from releasing a lock. Lock stealing should not be used as the primary mechanism in which peer clients coordinate biometric sensor use.

6.6.2.2 Lock Stealing Prevention Period (LSPP)

To assist in coordinating access among clients and to prevent excessive lock stealing, a service may trigger a time period that forbids lock stealing for each sensor operation. For convenience, this period of time will be referred to as the lock stealing prevention period (LSPP).

During the LSPP, all attempts to steal the service lock will fail. Consequently, if a client experiences a fatal failure during a sensor operation, then all peer clients need to wait until the service re-enables lock stealing.

All services should implement a non-zero LSPP. The recommended time for the LSPP is on the order of 100 seconds. Services that enforce an LSPP must start the LSPP immediately before sovereign sensor control is required. Conversely, services should not enforce an LSPP unless absolutely necessary.

If a request provides an invalid sessionId, then the operation should return an invalidId status instead of a failure—this must be true regardless of the LSPP threshold and whether or not it has expired. A failure signifies that the state of the service is still within the LSPP threshold and the provided sessionId is valid.

A service may reinitiate a LSPP when an operation yields an undesirable result, such as failure. This would allow a client to attempt to resubmit the request or recover without worrying about whether or not the lock is still owned by the client’s session.

An LSPP ends after a fixed amount of time has elapsed, unless another sensor operation restarts the LSPP. Services should keep the length of the LSPP fixed throughout the service’s lifecycle. It is recognized, however, that there may be use cases in which a variable LSPP timespan is desirable or required. Regardless, when determining the appropriate timespan, implementers should carefully consider the tradeoffs between preventing excessive lock stealing, versus forcing all clients to wait until a service re-enables lock stealing.

6.6.2.3 Cancellation & (Lack of) Client Notification

Lock stealing must have no effect on any currently running sensor operations. It is possible that a client initiates a sensor operation, has its lock stolen away, yet the operation completes successfully. Subsequent sensor operations would yield a lockNotHeld status, which a client could use to indicate that their lock was stolen away from them. Services should be implemented such that the LSPP is longer than any sensor operation.

6.6.3 Unique Knowledge

As specified, the steal lock operation cannot be used to provide or obtain knowledge about unique characteristics of a client or service.

6.6.4 Return Values Detail

The steal lock operation must return a Result according to the following constraints.

6.6.4.1 Success

Status Value	success
Condition	The service was successfully locked to the provided session id.
Required Elements	status (Status, §3.12) the literal “success”
Optional Elements	None

See §2.4.5 for detailed information about the WS-BD concurrency and locking model. Cancellation must have no effect on pending sensor operations (§6.6.2.3).

6.6.4.2 Failure

Status Value	failure
Condition	The service could not be locked to the provided session id.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

Most steal lock operations that yield a failure status will do so because the service receives a lock stealing request during a lock stealing prevention period (§6.6.2.2). Services must also reserve a failure status for other non-LSPP failures that prevent the acquisition of the lock.

Implementers may choose to use the optional message field to provide more information to an end-user as to the specific reasons for the failure. However (as with all other failure status results), clients must not depend on any particular content to make this distinction.

6.6.4.3 Invalid Id

Status Value	invalidId
Condition	The provided session id is not registered with the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.6.4.4 Bad Value

Status Value	badValue
Condition	The provided session id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.7 Unlock

Description	Release the service lock
URL Template	/lock/{sessionId}
HTTP Method	DELETE
URL Parameters	{sessionId} (UUID, §3.2) Identity of the session releasing the service lock
Input Payload	None
Idempotent	Yes
Sensor Operation	No

6.7.1 Result Summary

success	status="success"
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId" badFields={"sessionId"} (StringArray, §3.7)
badValue	status="badValue" badFields={"sessionId"} (StringArray, §3.7)

6.7.2 Usage Notes

The unlock operation releases a service lock, making locking available to other clients.

See §2.4.5 for detailed information about the WS-BD concurrency and locking model.

6.7.3 Unique Knowledge

As specified, the unlock operation cannot be used to provide or obtain knowledge about unique characteristics of a client or service.

6.7.4 Return Values Detail

The steal lock operation must return a Result according to the following constraints.

6.7.4.1 Success

Status Value	success
Condition	The service returned to an unlocked state.
Required Elements	status (Status, §3.12) the literal “success”
Optional Elements	None

Upon releasing the lock, a client is no longer permitted to perform any sensor operations (§2.4.5). By idempotency (§2.4.7), if a client already has released the lock, subsequent unlock operations should also return success.

6.7.4.2 Failure

Status Value	failure
Condition	The service could not be transitioned into an unlocked state.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

Services must reserve a failure status to report system or internal failures and prevent the release of the service lock. The occurrence of unlock operations that fail is expected to be rare.

6.7.4.3 Invalid Id

Status Value	invalidId
Condition	The provided session id is not registered with the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.7.4.4 Bad Value

Status Value	badValue
Condition	The provided session id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.8 Get Service Info

Description	Retrieve metadata about the service that does not depend on session-specific information, or sovereign control of the target biometric sensor
URL Template	/info
HTTP Method	GET
URL Parameters	None
Input Payload	None
Idempotent	Yes
Sensor Operation	No

6.8.1 Result Summary

success

status="success"

metadata=dictionary containing service metadata (Dictionary, §3.3)

failure

status="failure"

message*=informative message describing failure

6.8.2 Usage Notes

The get service info operation provides information about the service and target biometric sensor. This operation must return information that is both (a) independent of session, and (b) does not require sovereign biometric sensor control. In other words, services must not control the target biometric sensor during a get service info operation itself. Implementations may (and are encouraged to) use service startup time to query the biometric sensor directly to create a cache of information and capabilities for get service info operations. The service should keep a cache of sensor and service metadata to reduce the amount of operations that query the sensor as this can be a lengthy operation.

The get service info operation does not require that a client be registered with the service. Unlike other operations, it does not take a session id as a URL parameter.

See §4.1 for information about the metadata returned from this operation.

Example: The following represents a ‘raw’ request to get the service’s metadata.

GET http://10.0.0.8:8000/Service/info HTTP/1.1

Content-Type: application/xml

Host: 10.0.0.8:8000

Example: The following is the ‘raw’ response from the above request. The metadata element of the result contains a Dictionary (§3.3) of parameter names and parameter information represented as a Parameter (§3.4).

HTTP/1.1 200 OK

Content-Length: 4244

Content-Type: application/xml; charset=utf-8

Server: Microsoft-HTTPAPI/2.0

Date: Tue, 03 Jan 2012 14:54:51 GMT

<status>success</status>

<item>

<key>width</key>

<name>width</name>

<q:type xmlns:q="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0" xmlns:a="http://www.w3.org/2001/XMLSchema">a:unsignedInt</q:type>

</allowedValues>

</value>

</item>

<item>

<key>height</key>

<name>height</name>

<q:type xmlns:q="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0" xmlns:a="http://www.w3.org/2001/XMLSchema">a:unsignedInt</q:type>

</allowedValues>

</value>

</item>

<item>

<key>frameRate</key>

<name>frameRate</name>

<q:type xmlns:q="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0" xmlns:a="http://www.w3.org/2001/XMLSchema">a:unsignedInt</q:type>

</allowedValues>

</value>

</item>

<item>

<key>modality</key>

<name>modality</name>

<q:type xmlns:q="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0" xmlns:a="http://www.w3.org/2001/XMLSchema">a:string</q:type>

</value>

</item>

<item>

<key>submodality</key>

<name>submodality</name>

<q:type xmlns:q="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0" xmlns:a="http://www.w3.org/2001/XMLSchema">a:string</q:type>

<defaultValue i:type="a:string" xmlns:a="http://www.w3.org/2001/XMLSchema">frontalFace</defaultValue>

</value>

</item>

</metadata>

</result>

6.8.3 Unique Knowledge

As specified, the get service info can be used to obtain knowledge about unique characteristics of a service. Through get service info, a service may expose implementation and/or service-specific configuration parameter names and values that are not defined in this specification (see Appendix A for further information on parameters).

6.8.4 Return Values Detail

The get service info operation must return a Result according to the following constraints.

6.8.4.1 Success

Status Value	success
Condition	The service provides service metadata
Required Elements	status (Status, §3.12) the literal "success" metadata (Dictionary, §3.3) information about the service metadata
Optional Elements	None

6.8.4.2 Failure

Status Value	failure
Condition	The service cannot provide service metadata
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

6.9 Initialize

Description	Initialize the target biometric sensor
URL Template	/initialize/{sessionId}
HTTP Method	POST
URL Parameters	{sessionId} (UUID, §3.2) Identity of the session requesting initialization
Input Payload	None
Idempotent	Yes
Sensor Operation	Yes

6.9.1 Result Summary

success	status="success"
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId" badFields={"sessionId"} (StringArray, §3.7)
canceled	status="canceled"
canceledWithSensorFailure	status="canceledWithSensorFailure"
sensorFailure	status="sensorFailure"
lockNotHeld	status="lockNotHeld"
lockHeldByAnother	status="lockHeldByAnother"
sensorBusy	status="sensorBusy"
sensorTimeout	status="sensorTimeout"
badValue	status="badValue" badFields={"sessionId"} (StringArray, §3.7)

6.9.2 Usage Notes

The initialize operation prepares the target biometric sensor for (other) sensor operations.

Some biometric sensors have no requirement for explicit initialization. In that case, the service should immediately return a success result.

Although not strictly necessary, services should directly map this operation to the initialization of the target biometric sensor, unless the service can reliably determine that the target biometric sensor is in a fully operational state. In other words, a service may decide to immediately return success if there is a reliable way to detect if the target biometric sensor is currently in an initialized state. This style of “short circuit” evaluation could reduce initialization times. However, a service that always initializes the target biometric sensor would enable the ability of a client to attempt a manual reset of a sensor that has entered a faulty state. This is particularly useful in physically separated service implementations where the connection between the target biometric sensor and the web service host may be less reliable than an integrated implementation.

6.9.3 Unique Knowledge

As specified, the initialize operation cannot be used to provide or obtain knowledge about unique characteristics of a client or service.

6.9.4 Return Values Detail

6.9.4.1 Success

Status Value	success
Condition	The service successfully initialized the target biometric sensor
Required Elements	status must be populated with the Status literal "success"
Optional Elements	None

6.9.4.2 Failure

Status Value	failure
Condition	The service experienced a fault that prevented successful initialization.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

A failure status must only be used to report failures that occurred within the web service, not within the target biometric sensor (§6.9.4.5, §6.9.4.6)

6.9.4.3 Invalid Id

Status Value	invalidId
Condition	The provided session id is not registered with the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.9.4.4 Canceled

Status Value	canceled
Condition	The initialization operation was interrupted by a cancellation request.
Required Elements	status (Status, §3.12) the literal “canceled”
Optional Elements	None

See §6.16.2.2 for information about what may trigger a cancellation.

6.9.4.5 Canceled with Sensor Failure

Status Value	canceledWithSensorFailure
Condition	The initialization operation was interrupted by a cancellation request and the target biometric sensor experienced a failure
Required Elements	status (Status, §3.12) the literal “canceledWithSensorFailure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

Services must return a canceledWithSensorFailure result if a cancellation request caused a failure within the target biometric sensor. Clients receiving this result may need to reattempt the initialization request to restore full functionality. See §6.16.2.2 for information about what may trigger a cancellation.

6.9.4.6 Sensor Failure

Status Value	sensorFailure
Condition	The initialization failed due to a failure within the target biometric sensor
Required Elements	status (Status, §3.12) the literal “sensorFailure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

A sensorFailure status must only be used to report failures that occurred within the target biometric sensor, not a failure within the web service (§6.9.4.2).

6.9.4.7 Lock Not Held

Status Value	lockNotHeld
Condition	Initialization could not be performed because the requesting client does not hold the lock
Required Elements	status (Status, §3.12) the literal “lockNotHeld”
Optional Elements	None

Sensor operations require that the requesting client holds the service lock.

6.9.4.8 Lock Held by Another

Status Value	lockHeldByAnother
Condition	Initialization could not be performed because the lock is held by another client.
Required Elements	status (Status, §3.12) the literal “lockHeldByAnother”
Optional Elements	None

6.9.4.9 Sensor Busy

Status Value	sensorBusy
Condition	Initialization could not be performed because the service is already performing a different sensor operation for the requesting client.
Required Elements	status (Status, §3.12) the literal “sensorBusy”
Optional Elements	None

6.9.4.10 Sensor Timeout

Status Value	sensorTimeout
Condition	Initialization could not be performed because the target biometric sensor took too long to complete the initialization request.
Required Elements	status (Status, §3.12) the literal “sensorTimeout”
Optional Elements	None

A service did not receive a timely response from the target biometric sensor. Note that this condition is distinct from the client’s originating HTTP request, which may have its own, independent timeout. (See A.2 for information on how a client might determine timeouts.)

6.9.4.11 Bad Value

Status Value	badValue
Condition	The provided session id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.10 Get Configuration

Description	Retrieve metadata about the target biometric sensor’s current configuration
URL Template	/configure/{sessionId}
HTTP Method	GET
URL Parameters	{sessionId} (UUID, §3.2) Identity of the session requesting the configuration
Input Payload	None
Idempotent	Yes
Sensor Operation	Yes

6.10.1 Result Summary

success	status="success" metadata=current configuration of the sensor (Dictionary, §3.3)
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId" badFields={"sessionId"} (StringArray, §3.7)
canceled	status="canceled"
canceledWithSensorFailure	status="canceledWithSensorFailure"
sensorFailure	status="sensorFailure"
lockNotHeld	status="lockNotHeld"
lockHeldByAnother	status="lockHeldByAnother"
initializationNeeded	status="initializationNeeded"
configurationNeeded	status="configurationNeeded"
sensorBusy	status="sensorBusy"
sensorTimeout	status="sensorTimeout"
badValue	status="badValue" badFields={"sessionId"} (StringArray, §3.7)

6.10.2 Usage Notes

The get configuration operation retrieves the service’s current configuration.

Example: The following represents a ‘raw’ request to retrieve the current configuration information of the service.

GET http://10.0.0.8:8000/Service/configure/d745cd19-facd-4f91-8774-aac5ca9766a2 HTTP/1.1

Content-Type: application/xml

Host: 10.0.0.8:8000

Example: The following is the ‘raw’ response from the previous request. The metadata element in the result contains a Dictionary (§3.3) of parameter names and their respective values.

HTTP/1.1 200 OK

Content-Length: 554

Content-Type: application/xml; charset=utf-8

Server: Microsoft-HTTPAPI/2.0

Date: Tue, 03 Jan 2012 14:57:29 GMT

<result xmlns="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0"

xmlns:i="http://www.w3.org/2001/XMLSchema-instance">

<status>success</status>

<item>

<key>width</key>

</item>

<item>

<key>height</key>

</item>

<item>

<key>frameRate</key>

</item>

</metadata>

</result>

6.10.3 Unique Knowledge

As specified, the get configuration can be used to obtain knowledge about unique characteristics of a service. Through get configuration, a service may expose implementation and/or service-specific configuration parameter names and values that are not explicitly described in this document.

6.10.4 Return Values Detail

The get configuration operation must return a Result according to the following constraints.

6.10.4.1 Success

Status Value	success
Condition	The service provides the current configuration
Required Elements	status (Status, §3.12) the literal “success” metadata (Dictionary, §3.3) the target biometric sensor’s current configuration
Optional Elements	None

See §4.2 for information regarding configurations.

6.10.4.2 Failure

Status Value	failure
Condition	The service cannot provide the current configuration due to service (not target biometric sensor) error.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

Services must only use this status to report failures that occur within the web service, not the target biometric sensor (see §6.10.4.5, §6.10.4.6).

6.10.4.3 Invalid Id

Status Value	invalidId
Condition	The provided session id is not registered with the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.10.4.4 Canceled

Status Value	canceled
Condition	The get configuration operation was interrupted by a cancellation request.
Required Elements	status (Status, §3.12) the literal “canceled”
Optional Elements	None

See §6.16.2.2 for information about what may trigger a cancellation.

6.10.4.5 Canceled with Sensor Failure

Status Value	canceledWithSensorFailure
Condition	The get configuration operation was interrupted by a cancellation request during which the target biometric sensor experienced a failure
Required Elements	status (Status, §3.12) the literal “canceledWithSensorFailure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

Services must return a canceledWithSensorFailure result if a cancellation request caused a failure within the target biometric sensor. Clients receiving this result may need to perform initialization to restore full functionality. See §6.16.2.2 for information about what may trigger a cancellation.

6.10.4.6 Sensor Failure

Status Value	sensorFailure
Condition	The configuration could not be queried due to a failure within the target biometric sensor.
Required Elements	status (Status, §3.12) the literal “sensorFailure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

A sensorFailure status must only be used to report failures that occurred within the target biometric sensor, not a failure within the web service (§6.9.4.2).

6.10.4.7 Lock Not Held

Status Value	lockNotHeld
Condition	The configuration could not be queried because the requesting client does not hold the lock.
Required Elements	status (Status, §3.12) the literal “lockNotHeld”
Optional Elements	None

Sensor operations require that the requesting client holds the service lock.

6.10.4.8 Lock Held by Another

Status Value	lockHeldByAnother
Condition	The configuration could not be queried because the lock is held by another client.
Required Elements	status (Status, §3.12) the literal “lockHeldByAnother”
Optional Elements	None

6.10.4.9 Initialization Needed

Status Value	initializationNeeded
Condition	The configuration could not be queried because the target biometric sensor has not been initialized.
Required Elements	status (Status, §3.12) the literal “initializationNeeded”
Optional Elements	None

Services should be able to provide the sensors configuration without initialization; however, this is not strictly necessary. Regardless, robust clients should assume that configuration will require initialization.

6.10.4.10 Configuration Needed

Status Value	configurationNeeded
Condition	The configuration could not be queried because the target biometric sensor has not been initialized.
Required Elements	status (Status, §3.12) the literal “configurationNeeded”
Optional Elements	None

Services may require configuration to be set before a configuration can be retrieved if a service does not provide a valid default configuration.

6.10.4.11 Sensor Busy

Status Value	sensorBusy
Condition	The configuration could not be queried because the service is already performing a different sensor operation for the requesting client.
Required Elements	status (Status, §3.12) the literal “sensorBusy”
Optional Elements	None

6.10.4.12 Sensor Timeout

Status Value	sensorTimeout
Condition	The configuration could not be queried because the target biometric sensor took too long to complete the request.
Required Elements	status (Status, §3.12) the literal “sensorTimeout”
Optional Elements	None

6.10.4.13 Bad Value

Status Value	badValue
Condition	The provided session id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.11 Set Configuration

Description	Set the target biometric sensor’s configuration
URL Template	/configure/{sessionId}
HTTP Method	POST
URL Parameters	{sessionId} (UUID, §3.2) Identity of the session setting the configuration
Input Payload	Desired sensor configuration (Dictionary, §3.3)
Idempotent	Yes
Sensor Operation	Yes

6.11.1 Result Summary

success	status="success"
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId" badFields={"sessionId"} (StringArray, §3.7)
canceled	status="canceled"
canceledWithSensorFailure	status="canceledWithSensorFailure"
sensorFailure	status="sensorFailure"
lockNotHeld	status="lockNotHeld"
lockHeldByAnother	status="lockHeldByAnother"
initializationNeeded	status="initializationNeeded"
sensorBusy	status="sensorBusy"
sensorTimeout	status="sensorTimeout"
unsupported	status="unsupported" badFields={field names} (StringArray, §3.7)
badValue	status="badValue" badFields={"sessionId"} (StringArray, §3.7) (or) status="badValue" badFields={field names} (StringArray, §3.7)
noSuchParameter	status="unsupported" badFields={field names} (StringArray, §3.7)

6.11.2 Usage Notes

The set configuration operation sets the configuration of a service’s target biometric sensor.

6.11.2.1 Input Payload Information

The set configuration operation is the only operation that takes input within the body of the HTTP request. The desired configuration must be sent as a single Dictionary (§3.3) element named configuration. See §4.2 for information regarding configurations. See Appendix A for a complete XML Schema for this specification. The root element of the configuration data must conform to the following XML definition:

<xs:element name="configuration" type="wsbd:Dictionary" nillable="true"/>

Example: The following represents a ‘raw’ request to configure a service at http://10.0.0.8:8000/Sensor such that width=800, height=600, and frameRate=15. (In this example, each value element contains fully qualified namespace information, although this is not necessary.)

POST http://10.0.0.8:8000/Service/configure/d745cd19-facd-4f91-8774-aac5ca9766a2 HTTP/1.1

Content-Type: application/xml

Host: 10.0.0.8:8000

Content-Length: 459

Expect: 100-continue

<item>

<key>width</key>

</item>

<item>

<key>height</key>

</item>

<item>

<key>frameRate</key>

</item>

</configuration>

More information regarding the use of the xmlns attribute can be found in [XMLNS].

6.11.3 Unique Knowledge

The set configuration can be used to provide knowledge about unique characteristics to a service. Through set configuration, a client may provide implementation and/or service-specific parameter names and values that are not defined in this specification (see Appendix A for further information on parameters).

6.11.4 Return Values Detail

The set configuration operation must return a Result according to the following constraints.

6.11.4.1 Success

Status Value	success
Condition	The service was able to successfully set the full configuration
Required Elements	status (Status, §3.12) the literal “success”
Optional Elements	None

6.11.4.2 Failure

Status Value	failure
Condition	The service cannot set the desired configuration due to service (not target biometric sensor) error.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

Services must only use this status to report failures that occur within the web service, not the target biometric sensor (see §6.11.4.5, §6.11.4.6).

6.11.4.3 Invalid Id

Status Value	invalidId
Condition	The provided session id is not registered with the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

6.11.4.4 Canceled

Status Value	canceled
Condition	The set configuration operation was interrupted by a cancellation request.
Required Elements	status (Status, §3.12) the literal “canceled”
Optional Elements	None

See §6.16.2.2 for information about what may trigger a cancellation.

6.11.4.5 Canceled with Sensor Failure

Status Value	canceledWithSensorFailure
Condition	The set configuration operation was interrupted by a cancellation request during which the target biometric sensor experienced a failure
Required Elements	status (Status, §3.12) the literal “canceledWithSensorFailure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

6.11.4.6 Sensor Failure

Status Value	sensorFailure
Condition	The configuration could not be set due to a failure within the target biometric sensor.
Required Elements	status (Status, §3.12) the literal “sensorFailure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

A sensorFailure status must only be used to report failures that occurred within the target biometric sensor, not a failure within the web service (§6.11.4.2). Errors with the configuration itself should be reported via an unsupported (§6.11.4.12), badValue (§6.11.4.13), or badValue status (§6.11.4.14).

6.11.4.7 Lock Not Held

Status Value	lockNotHeld
Condition	The configuration could not be queried because the requesting client does not hold the lock.
Required Elements	status (Status, §3.12) the literal “lockNotHeld”
Optional Elements	None

Sensor operations require that the requesting client holds the service lock.

6.11.4.8 Lock Held by Another

Status Value	lockHeldByAnother
Condition	The configuration could not be set because the lock is held by another client.
Required Elements	status (Status, §3.12) the literal “lockHeldByAnother”
Optional Elements	None

6.11.4.9 Initialization Needed

Status Value	initializationNeeded
Condition	The configuration could not be set because the target biometric sensor has not been initialized.
Required Elements	status (Status, §3.12) the literal “initializationNeeded”
Optional Elements	None

Services should be able to set the configuration without initialization; however, this is not strictly necessary. Similarly, clients should assume that setting configuration will require initialization.

6.11.4.10 Sensor Busy

Status Value	sensorBusy
Condition	The configuration could not be set because the service is already performing a different sensor operation for the requesting client.
Required Elements	status (Status, §3.12) the literal “sensorBusy”
Optional Elements	None

6.11.4.11 Sensor Timeout

Status Value	sensorTimeout
Condition	The configuration could not be set because the target biometric sensor took too long to complete the request.
Required Elements	status (Status, §3.12) the literal “sensorTimeout”
Optional Elements	None

6.11.4.12 Unsupported

Status Value	unsupported
Condition	The requested configuration contains one or more values that are syntactically and semantically valid, but not supported by the service.
Required Elements	status (Status, §3.12) the literal “unsupported” badFields (StringArray, §3.7) an array that contains the field name(s) that corresponding to the unsupported value(s)
Optional Elements	None

Returning multiple fields allows a service to indicate that a particular combination of parameters is not supported by a service. See §6.1.2 for additional information on how services must handle parameter failures.

Example: A WS-BD service utilizes a very basic off-the-shelf web camera with limited capabilities. This camera has three parameters that are all dependent on each other: ImageHeight, ImageWidth, and FrameRate. The respective allowed values for each parameter might look like: {240, 480, 600, 768}, {320, 640, 800, 1024}, and {5, 10, 15, 20, 30}. Configuring the sensor will return unsupported when the client tries to set ImageHeight=768, ImageWidth=1024, and FrameRate=30; this camera might not support capturing images of a higher resolution at a fast frame rate. Another example is configuring the sensor to use ImageHeight=240 and ImageWidth=1024; as this is a very basic web camera, it might not support capturing images at this resolution. In both cases, the values provided for each parameter are individually valid but the overall validity is dependent on the combination of parameters

6.11.4.13 Bad Value

Status Value	badValue
Condition	Either: (a) The provided session id is not a well-formed UUID, or, (b) The requested configuration contains a parameter value that is either syntactically (e.g., an inappropriate data type) or semantically (e.g., a value outside of an acceptable range) invalid.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains either (a) the single field name, “sessionId”, or (b) the field name(s) that contain invalid value(s)
Optional Elements	None

Notice that for the set configuration operation, an invalid URL parameter or one or more invalid input payload parameters can trigger a badValue status.

See §6.1.2 for general information on how services must handle parameter failures.

6.11.4.14 No Such Parameter

Status Value	noSuchParameter
Condition	The requested configuration contains a parameter name that is not recognized by the service.
Required Elements	status (Status, §3.12) the literal “noSuchParameter” badFields (StringArray, §3.7) an array that contains the field name(s) that are not recognized by the service
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.12 Capture

Description	Capture biometric data
URL Template	/capture/{sessionId}
HTTP Method	POST
URL Parameters	{sessionId} (UUID, §3.2) Identity of the session requesting the capture
Input Payload	None
Idempotent	No
Sensor Operation	Yes

6.12.1 Result Summary

success	status="success" captureIds={identifiers of captured data} (UuidArray, §3.8)
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId" badFields={"sessionId"} (StringArray, §3.7)
canceled	status="canceled"
canceledWithSensorFailure	status="canceledWithSensorFailure"
sensorFailure	status="sensorFailure"
lockNotHeld	status="lockNotHeld"
lockHeldByAnother	status="lockHeldByAnother"
initializationNeeded	status="initializationNeeded"
configurationNeeded	status="configurationNeeded"
sensorBusy	status="sensorBusy"
sensorTimeout	status="sensorTimeout"
badValue	status="badValue" badFields={"sessionId"} (StringArray, §3.7)

6.12.2 Usage Notes

The capture operation triggers biometric acquisition. On success, the operation returns one or more identifiers, or capture ids. Naturally, the capture operation is not idempotent. Each capture operation returns unique identifiers—each execution returning references that are particular to that capture. Clients then can retrieve the captured data itself by passing a capture id as a URL parameter to the download operation.

Multiple capture ids are supported to accommodate sensors that return collections of biometric data. For example, a multi-sensor array might save an image per sensor. A mixed-modality sensor might assign a different capture id for each modality.

Important Note: The capture operation may include some post-acquisition processing. Although post-acquisition processing is directly tied to the capture operation, its effects are primarily on data transfer, and is therefore discussed in detail within the download operation documentation (§6.13.2.2)

6.12.2.1 Providing Timing Information

Depending on the sensor, a capture operation may take anywhere from milliseconds to tens of seconds to execute. (It is possible to have even longer running capture operations than this, but special accommodations may need to be made on the server and client side to compensate for typical HTTP timeouts.) By design, there is no explicit mechanism for a client to determine how long a capture operation will take. However, services can provide “hints” through capture timeout information (A.2.4), and clients can automatically adjust their own timeouts and behavior accordingly.

6.12.3 Unique Knowledge

As specified, the capture operation cannot be used to provide or obtain knowledge about unique characteristics of a client or service.

6.12.4 Return Values Detail

The capture operation must return a Result according to the following constraints.

6.12.4.1 Success

Status Value	success
Condition	The service successfully performed a biometric acquisition
Required Elements	status (Status, §3.12) the literal “success” captureIds (UuidArray, §3.8) one more UUIDs that uniquely identify the data acquired by the operation
Optional Elements	None

See the usage notes for capture (§6.12.2) and download (§6.13.2) for full detail.

6.12.4.2 Failure

Status Value	failure
Condition	The service cannot perform the capture due to a service (not target biometric sensor) error.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

Services must only use this status to report failures that occur within the web service, not the target biometric sensor (see §6.12.4.5, §6.12.4.6). A service may fail at capture if there is not enough internal storage available to accommodate the captured data (§A.3).

6.12.4.3 Invalid Id

Status Value	invalidId
Condition	The provided session id is not registered with the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.12.4.4 Canceled

Status Value	canceled
Condition	The capture operation was interrupted by a cancellation request.
Required Elements	status (Status, §3.12) the literal “canceled”
Optional Elements	None

See §6.16.2.2 for information about what may trigger a cancellation.

6.12.4.5 Canceled with Sensor Failure

Status Value	canceledWithSensorFailure
Condition	The capture operation was interrupted by a cancellation request during which the target biometric sensor experienced a failure
Required Elements	status (Status, §3.12) the literal “canceledWithSensorFailure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

6.12.4.6 Sensor Failure

Status Value	sensorFailure
Condition	The service could perform the capture due to a failure within the target biometric sensor.
Required Elements	status (Status, §3.12) the literal “sensorFailure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

A sensorFailure status must only be used to report failures that occurred within the target biometric sensor, not a failure within the web service (§6.12.4.2).

6.12.4.7 Lock Not Held

Status Value	lockNotHeld
Condition	The service could not perform a capture because the requesting client does not hold the lock.
Required Elements	status (Status, §3.12) the literal “lockNotHeld”
Optional Elements	None

Sensor operations require that the requesting client holds the service lock.

6.12.4.8 Lock Held by Another

Status Value	lockHeldByAnother
Condition	The service could not perform a capture because the lock is held by another client.
Required Elements	status (Status, §3.12) the literal “lockHeldByAnother”
Optional Elements	None

6.12.4.9 Initialization Needed

Status Value	initializationNeeded
Condition	The service could not perform a capture because the target biometric sensor has not been initialized.
Required Elements	status (Status, §3.12) the literal “initializationNeeded”
Optional Elements	None

Services should be able perform capture without explicit initialization. However, the specification recognizes that this is not always possible, particularly for physically separated implementations. Regardless, for robustness, clients should assume that setting configuration will require initialization.

6.12.4.10 Configuration Needed

Status Value	configurationNeeded
Condition	The capture could not be set because the target biometric sensor has not been configured.
Required Elements	status (Status, §3.12) the literal “configurationNeeded”
Optional Elements	None

A service should offer a default configuration to allow capture to be performed without an explicit configuration. Regardless, for robustness, clients should assume that capture requires configuration.

6.12.4.11 Sensor Busy

Status Value	sensorBusy
Condition	The service could not perform a capture because the service is already performing a different sensor operation for the requesting client.
Required Elements	status (Status, §3.12) the literal “sensorBusy”
Optional Elements	None

6.12.4.12 Sensor Timeout

Status Value	sensorTimeout
Condition	The service could not perform a capture because the target biometric sensor took too long to complete the request.
Required Elements	status (Status, §3.12) the literal “sensorTimeout”
Optional Elements	None

A service did not receive a timely response from the target biometric sensor. Note that this condition is distinct from the client’s originating HTTP request, which may have its own, independent timeout. (See §A.2 for information on how a client might determine timeouts.)

6.12.4.13 Bad Value

Status Value	badValue
Condition	The provided session id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.13 Download

Description	Download the captured biometric data
URL Template	/download/{captureId}
HTTP Method	GET
URL Parameters	{captureId} (UUID, §3.2) Identity of the captured data to download
Input Payload	None
Idempotent	Yes
Sensor Operation	No

6.13.1 Result Summary

success	status="success" metadata=sensor configuration at the time of capture (Dictionary, §3.3) sensorData=biometric data (xs:base64Binary)
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId" badFields={"captureId"} (StringArray, §3.7)
badValue	status="badValue" badFields={"captureId"} (StringArray, §3.7)
preparingDownload	status="preparingDownload"

6.13.2 Usage Notes

The download operation allows a client to retrieve biometric data acquired during a particular capture.

6.13.2.1 Capture and Download as Separate Operations

WS-BD decouples the acquisition operation (capture) from the data transfer (download) operation. This has two key benefits. First, it is a better fit for services that have post-acquisition processes. Second, it allows multiple clients to download the captured biometric data by exploiting the concurrent nature of HTTP. By making download a simple data transfer operation, service can handle multiple, concurrent downloads without requiring locking.

6.13.2.2 Services with Post-Acquisition Processing

A service does not need to make the captured data available immediately after capture; a service may have distinct acquisition and post-acquisition processes. The following are two examples of such services:

Example: A service exposing a fingerprint scanner also performs post processing on a fingerprint image—segmentation, quality assessment, and templatization.

Example: A service exposes a digital camera in which the captured image is not immediately available after a photo is taken; the image may need to be downloaded from to the camera’s internal storage or from the camera to the host computer (in a physically separated implementation). If the digital camera was unavailable for an operation due to a data transfer, a client requesting a sensor operation would receive a sensorBusy status.

The first method is to perform the post-processing within the capture operation itself. I.e., capture not only blocks for the acquisition to be performed, but also blocks for the post-processing—returning when the post-processing is complete. This type of capture is the easier of the two to both (a) implement on the client, and (b) use by a client.

Example: Figure 9 illustrates an example of a capture operation that includes post-processing. Once the post-processing is complete, capture ids are returned to the client.

Figure 9. Including post-processing in the capture operation means downloads are immediately available when capture completes. Unless specified, the status of all returned operations is success.

In the second method, post-processing may be performed by the web service after the capture operation returns. Capture ids are still returned to the client, but are in an intermediate state. This exposes a window of time in which the capture is complete, but the biometric data is not yet ready for retrieval or download. Data-related operations (download, get download info, and thrifty download) performed within this window return a preparingDownload status to clients to indicate that the captured data is currently in an intermediate state—captured, but not yet ready for retrieval.

Example: Figure 10 illustrates an example of a capture operation with separate post-processing. Returning to the example of the fingerprint scanner that transforms a raw biometric sample into a template after acquisition, assume that the service performs templatization after capture returns. During post-processing, requests for the captured data return preparingDownload, but the sensor itself is available for another capture operation.

Figure 10. Example of capture with separate post-acquisition processing that does involve the target biometric sensor. Because the post-acquisition processing does not involve the target biometric sensor, it is available for sensor operations. Unless specified, the status of all returned operations is success.

Services with an independent post-processing step should perform the post-processing on an independent unit of execution (e.g., a separate thread, or process). However, post-processing may include a sensor operation, which would interfere with incoming sensor requests.

Example: Figure 11 illustrates another variation on a capture operation with separate post-processing. Return to the digital camera example, but assume that it is a physically separate implementation and capture operation returns immediately after acquisition. The service also has a post-acquisition process that downloads the image data from the camera to a computer. Like the previous example, during post-processing, requests for the captured data return preparingDownload. However, the sensor is not available for additional operations because the post-processing step requires complete control over the camera to transfer the images to the host machine: preparing them for download.

Figure 11. Example of capture with separate post-acquisition processing that does involve the target biometric sensor. Because the post-acquisition processing does not involve the target biometric sensor, it is available for sensor operations. Unless specified, the status of all returned operations is success.

Unless there is an advantage to doing so, when post-acquisition processing includes a sensor operation, implementers should avoid having a capture operation that returns directly after acquisition. In this case, even when the capture operation finishes, clients cannot perform a sensor operation until the post-acquisition processing is complete.

In general, implementers should try to combine both the acquisition and post-acquisition processing into one capture operation—particularly if the delay due to post-acquisition processing is either operationally acceptable or a relatively insignificant contributor to the combined time.

A download operation must return failure if the post-acquisition processing cannot be completed successfully. Such failures cannot be reflected in the originating capture operation —that operation has already returned successfully with capture ids. Services must eventually resolve all preparingDownload statuses to success or failure. Through get service info, a service can provide information to a client on how long to wait after capture until a preparingDownload is fully resolved.

6.13.2.3 Client Notification

A client that receives a preparingDownload must poll the service until the requested data becomes available. However, through get service info, a service can provide “hints” to a client on how long to wait after capture until data can be downloaded (§A.2.5)

6.13.3 Unique Knowledge

The download operation can be used to provide metadata, which may be unique to the service, through the metadata element. See §4 for information regarding metadata.

6.13.4 Return Values Detail

The download operation must return a Result according to the following constraints.

6.13.4.1 Success

Status Value	success
Condition	The service can provide the requested data
Required Elements	status (Status, §3.12) the literal “success” metadata (Dictionary, §3.3) sensor metadata as it was at the time of capture sensorData (xs:base64Binary, [XSDPart2]) the biometric data corresponding to the requested capture id, base-64 encoded
Optional Elements	None

A successful download must populate the Result with all of the following information:

1. The status element must be populated with the Status literal “success”.

2. The metadata element must be populated with metadata of the biometric data and the configuration held by the target biometric sensor at the time of capture.

3. The sensorData element must contain the biometric data, base-64 encoded (xs:base64Binary), corresponding to the requested capture id.

See the usage notes for both capture (§6.12.2) and download (§6.13.2) for more detail regarding the conditions under which a service is permitted to accept or deny download requests.

6.13.4.2 Failure

Status Value	failure
Condition	The service cannot provide the requested data.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

A service might not be able to provide the requested data due to failure in post-acquisition processing, a corrupted data store or other service or storage related failure.

6.13.4.3 Invalid Id

Status Value	invalidId
Condition	The provided capture id is not recognized by the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “captureId”
Optional Elements	None

A capture id is invalid if it was not returned by a capture operation. A capture id may become unrecognized by the service automatically if the service automatically clears storage space to accommodate new captures (§A.3).

See §6.1.2 for general information on how services must handle parameter failures.

6.13.4.4 Bad Value

Status Value	badValue
Condition	The provided capture id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains the single field name, “captureId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.13.4.5 Preparing Download

Status Value	preparingDownload
Condition	The requested data cannot be provided because the service is currently performing a post-acquisition process—i.e., preparing it for download
Required Elements	status (Status, §3.12) the literal “preparingDownload”
Optional Elements	None

See the usage notes for both capture (§6.12.2) and download (§6.13.2) for full detail.

6.14 Get Download Info

Description	Get only the metadata associated with a particular capture
URL Template	/download/{captureId}/info
HTTP Method	GET
URL Parameters	{captureId} (UUID, §3.2) Identity of the captured data to query
Input Payload	Not applicable
Idempotent	Yes
Sensor Operation	No

6.14.1 Result Summary

success	status="success" metadata=sensor configuration at the time of capture
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId" badFields={"captureId"} (StringArray, §3.7)
badValue	status="badValue" badFields={"captureId"} (StringArray, §3.7)
preparingDownload	status="preparingDownload"

6.14.2 Usage Notes

Given the potential large size of some biometric data the get download info operation provides clients with a way to get information about the biometric data without needing to transfer the biometric data itself. It is logically equivalent to the download operation, but without any sensor data. Therefore, unless detailed otherwise, the usage notes for download (§6.14.2) also apply to get download info.

6.14.3 Unique Knowledge

The get download info operation can be used to provide metadata, which may be unique to the service, through the metadata element. See §4 for information regarding metadata.

6.14.4 Return Values Detail

The get download info operation must return a Result according to the following constraints.

6.14.4.1 Success

Status Value	success
Condition	The service can provide the requested data
Required Elements	status (Status, §3.12) the literal “success” metadata (Dictionary, §3.3) the sensor’s configuration as it was set at the time of capture
Optional Elements	None

A successful get download info operation returns all of the same information as a successful download operation (§6.13.4.1), but without the sensor data.

6.14.4.2 Failure

Status Value	failure
Condition	The service cannot provide the requested data.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

A service might not be able to provide the requested data due to failure in post-acquisition processing, a corrupted data store or other service or storage related failure.

6.14.4.3 Invalid Id

Status Value	invalidId
Condition	The provided capture id is not recognized by the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “captureId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.14.4.4 Bad Value

Status Value	badValue
Condition	The provided capture id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains the single field name, “captureId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.14.4.5 Preparing Download

Status Value	preparingDownload
Condition	The requested data cannot be provided because the service is currently performing a post-acquisition process—i.e., preparing it for download
Required Elements	status (Status, §3.12) the literal “preparingDownload”
Optional Elements	None

See the usage notes for both capture (§6.12.2) and download (§6.13.2) for full detail.

6.15 Thrifty Download

Description	Download a compact representation of the captured biometric data suitable for preview
URL Template	/download/{captureId}/{maxSize}
HTTP Method	GET
URL Parameters	{captureId} (UUID, §3.2) Identity of the captured data to download {maxSize} (xs:string, [XSDPart2]) Content-type dependent indicator of maximum permitted download size
Input Payload	None
Idempotent	Yes
Sensor Operation	No

6.15.1 Result Summary

success	status="success" metadata=minimal metadata describing the captured data (Dictionary, §3.3, §4.3.1) sensorData=biometric data (xs:base64Binary)
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId" badFields={"captureId"} (StringArray, §3.7)
badValue	status="badValue" badFields=either "captureId", "maxSize", or both (StringArray, §3.7)
unsupported	status="unsupported"
preparingDownload	status="preparingDownload"

6.15.2 Usage Notes

The thrifty download operation allows a client to retrieve a compact representation of the biometric data acquired during a particular capture. It is logically equivalent to the download operation, but provides a compact version of the sensor data. Therefore, unless detailed otherwise, the usage notes for download (§6.14.2) also apply to get download info.

The suitability of the thrifty download data as a biometric is implementation-dependent. For some applications, the compact representation may be suitable for use within a biometric algorithm; for others, it may only serve the purpose of preview.

For images, the maxSize parameter describes the maximum image width or height (in pixels) that the service may return; neither dimension shall exceed maxSize. It is expected that servers will dynamically scale the captured data to fulfill a client request. This is not strictly necessary, however, as long as the maximum size requirements are met.

For non-images, the default behavior is to return unsupported. It is possible to use URL parameter maxSize as general purpose parameter with implementation-dependent semantics. (See the next section for details.)

6.15.3 Unique Knowledge

The thrifty download operation can be used to provide knowledge about unique characteristics to a service. Through thrifty download, a service may (a) redefine the semantics of maxSize or (b) provide a data in a format that does not conform to the explicit types defined in this specification (see Appendix B for content types).

6.15.4 Return Values Detail

The thrifty download operation must return a Result according to the following constraints.

6.15.4.1 Success

Status Value	success
Condition	The service can provide the requested data
Required Elements	status (Status, §3.12) the literal “success” metadata (Dictionary, §3.3) minimal representation of sensor metadata as it was at the time of capture. See §4.3.1 for information regarding minimal metadata. sensorData (xs:base64Binary, [XSDPart2]) the biometric data corresponding to the requested capture id, base-64 encoded, scaled appropriately to the maxSize parameter.
Optional Elements	None

For increased efficiency, a successful thrifty download operation only returns the sensor data, and a subset of associated metadata. The metadata returned should be information that is absolutely essential to open or decode the returned sensor data.

6.15.4.2 Failure

Status Value	failure
Condition	The service cannot provide the requested data.
Required Elements	status (Status, §3.12) the literal “failure”
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

A service might not be able to provide the requested data due to a corrupted data store or other service or storage related failure.

6.15.4.3 Invalid Id

Status Value	invalidId
Condition	The provided capture id is not recognized by the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “captureId”
Optional Elements	None

A capture id is invalid if it does not correspond to a capture operation. A capture id may become unrecognized by the service automatically if the service automatically clears storage space to accommodate new captures (§A.3).

See §6.1.2 for general information on how services must handle parameter failures.

6.15.4.4 Bad Value

Status Value	badValue
Condition	The provided capture id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains one or both of the following fields: - “captureId” if the provided session id is not well-formed - “maxSize” if the provided maxSize parameter is not well-formed
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.15.4.5 Unsupported

Status Value	unsupported
Condition	The service does not support thrifty download,
Required Elements	status (Status, §3.12) the literal “unsupported”
Optional Elements	None

Services that capture biometrics that are not image-based should return unsupported.

6.15.4.6 Preparing Download

Status Value	preparingDownload
Condition	The requested data cannot be provided because the service is currently performing a post-acquisition process—i.e., preparing it for download
Required Elements	status (Status, §3.12) the literal “preparingDownload”
Optional Elements	None

Like download, the availability of thrifty download data may also be affected by the sequencing of post-acquisition processing. See §6.13.2.2 for detail.

6.16 Cancel

Description	Cancel the current sensor operation
URL Template	/cancel/{sessionId}
HTTP Method	POST
URL Parameters	{sessionId} (UUID, §3.2) Identity of the session requesting cancellation
Input Payload	None
Idempotent	Yes
Sensor Operation	Yes

6.16.1 Result Summary

success	status="success"
failure	status="failure" message*=informative message describing failure
invalidId	status="invalidId"
lockNotHeld	status="lockNotHeld"
lockHeldByAnother	status="lockHeldByAnother"
badValue	status="badValue" badFields={"sessionId"}

6.16.2 Usage Notes

The cancel operation stops any currently running sensor operation; it has no effect on non-sensor operations. If cancellation of an active sensor operation is successful, cancel operation receives a success result, while the canceled operation receives a canceled (or canceledWithSensorFailure) result. As long as the operation is canceled, the cancel operation itself receives a success result, regardless if cancellation caused a sensor failure. In other words, if cancellation caused a fault within the target biometric sensor, as long as the sensor operation has stopped running, the cancel operation is considered to be successful.

Figure 12. Example sequence of events for a client initially requesting a capture followed by a cancellation request.

All services must provide cancellation for all sensor operations.

6.16.2.1 Canceling Non-Sensor Operations

Clients are responsible for canceling all non-sensor operations via client-side mechanisms only. Cancellation of sensor operations requires a separate service operation, since a service may need to “manually” interrupt a busy sensor. A service that had its client terminate a non-sensor operation would have no way to easily determine that a cancellation was requested.

Figure 13. Cancellations of non-sensor operations do not require a cancel operation to be requested to the service. An example of this is where a client initiates then cancels a download operation.

6.16.2.2 Cancellation Triggers

Typically, the client that originates the sensor operation to be cancelled also initiates the cancellation request. Because WSBD operations are performed synchronously, cancellations are typically initiated on a separate unit of execution such as an independent thread or process.

Notice that the only requirement to perform cancellation is that the requesting client holds the service lock. It is not a requirement that the client that originates the sensor operation to be canceled also initiates the cancellation request. Therefore, it is possible that a client may cancel the sensor operation initiated by another client. This occurs if a peer client (a) manages to steal the service lock before the sensor operation is completed, or (b) is provided with the originating client’s session id.

A service might also self-initiate cancellation. In normal operation, a service that does not receive a timely response from a target biometric sensor would return sensorTimeout. However, if the service’s internal timeout mechanism fails, a service may initiate a cancel operation itself. Implementers should use this as a “last resort” compensating action.

In summary, clients should be designed to not expect to be able to match a cancelation notification to any specific request or operation.

6.16.3 Unique Knowledge

As specified, the cancel operation cannot be used to provide or obtain knowledge about unique characteristics of a client or service.

6.16.4 Return Values Detail

The cancel operation must return a Result according to the following constraints.

6.16.4.1 Success

Status Value	success
Condition	The service successfully canceled the sensor operation
Required Elements	status must be populated with the Status literal "success"
Optional Elements	None

See the usage notes for capture (§6.12.2) and download (§6.13.2) for full detail.

6.16.4.2 Failure

Status Value	failure
Condition	The service could not cancel the sensor operation
Required Elements	status (Status, §3.12) must be populated with the Status literal "failure"
Optional Elements	message (xs:string, [XSDPart2]) an informative description of the nature of the failure

Services should try to return failure in a timely fashion—there is little advantage to a client if it receives the cancellation failure after the sensor operation to be canceled completes.

6.16.4.3 Invalid Id

Status Value	invalidId
Condition	The provided session id is not recognized by the service.
Required Elements	status (Status, §3.12) the literal “invalidId” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

6.16.4.4 Lock Not Held

Status Value	lockNotHeld
Condition	The service could cancel the operation because the requesting client does not hold the lock.
Required Elements	status (Status, §3.12) the literal “lockNotHeld”
Optional Elements	None

Sensor operations require that the requesting client holds the service lock.

6.16.4.5 Lock Held by Another

Status Value	lockHeldByAnother
Condition	The service could not cancel the operation because the lock is held by another client.
Required Elements	status (Status, §3.12) the literal “lockHeldByAnother”
Optional Elements	None

6.16.4.6 Bad Value

Status Value	badValue
Condition	The provided session id is not a well-formed UUID.
Required Elements	status (Status, §3.12) the literal “badValue” badFields (StringArray, §3.7) an array that contains the single field name, “sessionId”
Optional Elements	None

See §6.1.2 for general information on how services must handle parameter failures.

7 Conformance Profiles

This section of the specification describes the requirements around conformance to the WS-Biometric Devices specification.

7.1.1 Conformance

Implementations claiming conformance to this specification, MUST make such a claim according to all three of the following factors.

1. If the implementation is general or modality specific

2. The operations that are implemented (§7.1.3)

3. If the implementation includes live preview (§5)

An implementation that is modality specific must implement the service information and configuration metadata according to their respective subsection. For example, a “fingerprint” conformant service must implement the service and configuration information according to §7.2. Note that it is possible to implement a fingerprint-based WS-Biometric Devices service without adhering to §7.2, however, such an implementation cannot claim modality specific conformance.

7.1.2 Language

Conformance claims must take the form

“WS-Biometric Devices [modality] Conformance Level n [L]”

where

· [modality] is optional phrase that indicates if the implementation is modality specific

· L* is an indicator if the implementation supports live preview.

· Square brackets, [ ], are indicator to the reader of this specification that the phrase is optional; they are not to be included in the claim itself

For example, the phrase “WS-Biometric Devices Conformance Level 3” indicates that the implementation is (a) not modality specific (b) implements the operations get service information, initialize, get configuration, capture, download, and get download information and (c) does NOT support live preview. Likewise, the phrase “WS-Biometric Devices Fingerprint Conformance Level 1L” indicates that the implementation (a) implements the service information and configuration parameters as specified by §7.2, (b) implements all operations and (c) supports live-preview.

For implementations that support multiple modalities, then there shall be a conformance claim for each modality. For example, a converged device that supports machine readable documents, fingerprint (according to §7.2) and iris (according to §7.4) might claim “WS-Biometric Devices Conformance Level 2, WS-Biometric Devices Fingerprint Conformance Level 3L, and WS-Biometric Devices Iris Conformance Level 1.”

7.1.3 Operations

The table below shows three levels of conformance to this specification. An ‘X’ represents that the operation requires functionality and implementation. For operations that lack the identifier, the service should implement the operation minimally by always returning success and related arbitrary data. Sending success and arbitrary data removes any concern from clients whether or not certain operations are supported by removing the responsibility of functionality and implementation from the implementer/service.

Operation Conformance Level	1	2	3
Register (§6.3)	X
Unregister (§6.4)	X
Try Lock (§6.5)	X
Steal Lock (§6.6)	X
Unlock (§6.7)	X
Get Service Information (§6.8)	X	X	X
Initialize (§6.9)	X	X	X
Get Configuration (§6.10)	X	X	X
Set Configuration (§6.11)	X	X
Capture (§6.12)	X	X	X
Download (§6.13)	X	X	X
Get Download Information (§6.14)	X	X	X
Thrifty Download (§6.15)	X	X
Cancel (§6.16)	X	X

7.1.3.1 Additional Supported Operations

Operation	Identifier
Live Preview (§5)	L

7.2 Fingerprint

7.2.1.1 Service Information

7.2.1.2 Submodality

Formal Name	submodality
Description	A distinct subtype of fingerprint modality, supported by the sensor.
Data Type	xs:string [XSDPart2]
Required	Yes
Allowed Values	RightThumbFlat RightIndexFlat RightMiddleFlat RightRingFlat RightLittleFlat LeftThumbFlat LeftIndexFlat LeftMiddleFlat LeftRingFlat LeftLittleFlat LeftSlap RightSlap ThumbsSlap RightThumbRolled RightIndexRolled RightMiddleRolled RightRingRolled RightLittleRolled LeftThumbRolled LeftIndexRolled LeftMiddleRolled LeftRingRolled LeftLittleRolled

7.2.1.3 Image Size

Formal Name	fingerprintImageSize
Description	*The width and height of a resulting fingerprint image, in pixels. If this value is calculated after capture, this shall* be the maximum width and height of a resulting image.**
Data Type	resolution [§3.9]
Required	Yes
Allowed Values	The width element can be any positive integer value. The height element can be any positive integer value. The unit element, if defined, must be “pixel” or “pixels”.

7.2.1.4 Image Content Type

Formal Name	fingerprintImageContentType
Description	The data format of the resulting fingerprint image.
Data Type	xs:string [XSDPart2]
Required	Yes
Allowed Values	Any string value conformant with Appendix B, §B.2.

7.2.1.5 Image Density

Formal Name	fingerprintImageDensity
Description	The pixel density of a resulting image represented in pixels per inch (PPI).
Data Type	xs:int [XSDPart2]
Required	Yes
Allowed Values	Any positive integer value.

7.3 Face

7.3.1 Service Information

7.3.1.1 Submodality

Formal Name	submodality
Description	A distinct subtype of face modality, supported by the sensor.
Data Type	xs:string [XSDPart2]
Required	Yes
Allowed Values	Face2d Face3d

7.3.1.2 Image Size

Formal Name	faceImageSize
Description	*The width and height of a resulting face image, in pixels. If this value is calculated after capture, this shall* be the maximum width and height of a resulting image.**
Data Type	resolution [§3.9]
Required	Yes
Allowed Values	The width element can be any positive integer value. The height element can be any positive integer value. The unit element, if defined, must be “pixel” or “pixels”.

7.3.1.3 Image Content Type

Formal Name	faceImageContentType
Description	The data format of the resulting face image.
Data Type	xs:string [XSDPart2]
Required	Yes
Allowed Values	Any string value conformant with Appendix B, §B.2.

7.4 Iris

7.4.1 Service Information

7.4.1.1 Submodality

Formal Name	submodality
Description	A distinct subtype of iris modality, supported by the sensor.
Data Type	xs:string [XSDPart2]
Required	Yes
Allowed Values	LeftIris RightIris BothIrises

7.4.1.2 Image Size

Formal Name	irisImageSize
Description	*The width and height of a resulting iris image, in pixels. If this value is calculated after capture, this shall* be the maximum width and height of a resulting image.**
Data Type	resolution [§3.9]
Required	Yes
Allowed Values	The width element can be any positive integer value. The height element can be any positive integer value. The unit element, if defined, must be “pixel” or “pixels”.

7.4.1.3 Image Content Type

Formal Name	irisImageContentType
Description	The data format of the resulting iris image.
Data Type	xs:string [XSDPart2]
Required	Yes
Allowed Values	Any string value conformant with Appendix B, §B.2.

Appendix A. Parameter Details

This appendix details the individual parameters available from a get service info operation. For each parameter, the following information is listed:

· The formal parameter name

· The expected data type of the parameter’s value

· If a the service is required to implement the parameter

A.1 Connections

The following parameters describe how the service handles session lifetimes and registrations.

A.1.1 Last Updated

Formal Name	lastUpdated
Data Type	xs:dateTime [XSDPart2]
Required	Yes

This parameter provides a timestamp of when the service last updated the common info parameters (this parameter not withstanding). The timestamp must include time zone information. Implementers should expect clients to use this timestamp to detect if any cached values of the (other) common info parameters may have changed.

A.1.2 Inactivity Timeout

Formal Name	inactivityTimeout
Data Type	xs:nonNegativeInteger [XSDPart2]
Required	Yes

This parameter describes how long, in seconds, a session can be inactive before it may be automatically closed by the service. A value of ‘0’ indicates that the service never drops sessions due to inactivity.

Inactivity time is measured per session. Services must measure it as the time elapsed between (a) the time at which a client initiated the session’s most recent operation and (b) the current time. Services must only use the session id to determine a session’s inactivity time. For example, a service does not maintain different inactivity timeouts for requests that use the same session id, but originate from two different IP addresses. Services may wait longer than the inactivity timeout to drop a session, but must not drop inactive sessions any sooner than the inactivityTimeout parameter indicates.

A.1.3 Maximum Concurrent Sessions

Formal Name	maximumConcurrentSessions
Data Type	xs:positiveInteger [XSDPart2]
Required	Yes

This parameter describes the maximum number of concurrent sessions a service can maintain. Upon startup, a service must have zero concurrent sessions. When a client registers successfully (§6.3), the service increases its count of concurrent sessions by one. After successful unregistration (§6.4), the service decreases its count of concurrent sessions by one .

A.1.4 Least Recently Used (LRU) Sessions Automatically Dropped

Formal Name	autoDropLRUSessions
Data Type	xs:boolean [XSDPart2]
Required	Yes

This parameter describes whether or not the service automatically unregisters the least-recently-used session when the service has reached its maximum number of concurrent sessions. If true, then upon receiving a registration request, the service may drop the least-recently used session if the maximum number of concurrent sessions has already been reached. If false, then any registration request that would cause the service to exceed its maximum number of concurrent sessions results in failure. The service shall not drop a session that currently holds the lock unless the session’s inactivity is outside of the inactivity timeout (§A.1.2) threshold.

A.2 Timeouts

Clients should not block indefinitely on any operation. However, since different services may differ significantly in the time they require to complete an operation, clients require a means to determine appropriate timeouts. The timeouts in this subsection describe how long a service waits until the service either returns sensorTimeout or initiates a service-side cancellation (§6.16.2.1). Services may wait longer than the times reported here, but, (under normal operations) must not report a sensorTimeout or initiate a cancellation before the reported time elapses. In other words, a client should be able to use these timeouts to help determine a reasonable upper bound on the time required for sensor operations.

Note that these timeouts do not include any round-trip and network delay—clients should add an additional window to accommodate delays unique to that particular client-server relationship.

A.2.1 Initialization Timeout

Formal Name	initializationTimeout
Data Type	xs:positiveInteger [XSDPart2]
Required	Yes

This parameter describes how long, in milliseconds, a service will wait for a target biometric sensor to perform initialization before it returns sensorTimeout (§6.9.4.10) or initiates a service-side cancellation (§6.16.2.1).

A.2.2 Get Configuration Timeout

Formal Name	getConfigurationTimeout
Data Type	xs:positiveInteger [XSDPart2]
Required	Yes

This parameter describes how long, in milliseconds, a service will wait for a target biometric sensor to retrieve its configuration before it returns sensorTimeout (§6.10.4.12) or initiates a service-side cancellation (§6.16.2.1).

A.2.3 Set Configuration Timeout

Formal Name	setConfigurationTimeout
Data Type	xs:positiveInteger [XSDPart2]
Required	Yes

This parameter describes how long, in milliseconds, a service will wait for a target biometric sensor to set its configuration before it returns sensorTimeout (§6.11.4.11) or initiates a service-side cancellation (§6.16.2.1).

A.2.4 Capture Timeout

Formal Name	captureTimeout
Data Type	xs:positiveInteger [XSDPart2]
Required	Yes

This parameter describes how long, in milliseconds, a service will wait for a target biometric sensor to perform biometric acquisition before it returns sensorTimeout (§6.11.4.11) or initiates a service-side cancellation (§6.16.2.1).

A.2.5 Post-Acquisition Processing Time

Formal Name	postAcquisitionProcessingTime
Data Type	xs:nonNegativeInteger [XSDPart2]
Required	Yes

This parameter describes an upper bound on how long, in milliseconds, a service takes to perform post-acquisition processing. A client should not expect to be able to download captured data before this time has elapsed. Conversely, this time also describes how long after a capture a server is permitted to return preparingDownload for the provided capture ids. A value of zero (‘0’) indicates that the service includes any post-acquisition processing within the capture operation or that no post-acquisition processing is performed.

A.2.6 Lock Stealing Prevention Period

Formal Name	lockStealingPreventionPeriod
Data Type	xs:nonNegativeInteger [XSDPart2]
Required	Yes

This parameter describes the length, in milliseconds, of the lock stealing prevention period (§6.6.2.2).

A.3 Storage

The following parameters describe how the service stores captured biometric data.

A.3.1 Maximum Storage Capacity

Formal Name	maximumStorageCapacity
Data Type	xs:positiveInteger [XSDPart2]
Required	Yes

This parameter describes how much data, in bytes, the service is capable of storing.

A.3.2 Least-Recently Used Capture Data Automatically Dropped

Formal Name	lruCaptureDataAutomaticallyDropped
Data Type	xs:boolean [XSDPart2]
Required	Yes

This parameter describes whether or not the service automatically deletes the least-recently-used capture to stay within its maximum storage capacity. If true, the service may automatically delete the least-recently used biometric data to accommodate for new data. If false, then any operation that would require the service to exceed its storage capacity would fail.

A.4 Sensor

The following parameters describe information about the sensor and its supporting features

A.4.1 Modality

Formal Name	modality
Data Type	xs:string [XSDPart2]
Required	Yes

This parameter describes which modality or modalities are supported by the sensor.

The following table enumerates the list of modalities, as defined in [CBEFF2010], which provides the valid values for this field for currently identified modalities. Implementations are not limited to the following values, but shall use them if such modality is exposed. For example, if an implementation is exposing fingerprint capture capability, “Finger” shall be used. If an implementation is exposing an unlisted modality, it may use another value.

Modality Value	Description
Scent	Information about the scent left by a subject
DNA	Information about a subject’s DNA
Ear	A subject’s ear image
Face	An image of the subject’s face, either in two or three dimensions
Finger	An image of one of more of the subject’s fingerprints
Foot	An image of one or both of the subject’s feet.
Vein	Information about a subject’s vein pattern
HandGeometry	The geometry of an subject’s hand
Iris	An image of one of both of the subject’s irises
Retina	An image of one or both of the subject’s retinas
Voice	Information about a subject’s voice
Gait	Information about a subject’s gait or ambulatory movement
Keystroke	Information about a subject’s typing patterns
LipMovement	Information about a subject’s lip movements
SignatureSign	Information about a subject’s signature or handwriting

A.4.2 Submodality

Formal Name	submodality
Data Type	xs:string [XSDPart2]
Required	Yes

This parameter describes which submodalities are supported by the sensor. See §7 for submodality requirements for a particular modality.

Appendix B. Content Type Data

This appendix contains a catalog of content types for use in conformance profiles and parameters. When possible, the identified data formats shall be used.

B.1 General Type

application/xml	Extensible Markup Language (XML) [XML]
text/plain	Plaintext [RFC2046]
text/xml	Extensible Markup Language (XML) [XML]

B.2 Image Formats

Refer to [CMediaType] for more information regarding a registered image type.

image/jpeg	Joint Photographics Experts Group [JPEG]
image/png	Portable Network Graphics [PNG]
image/tiff	Tagged Image File Format [TIFF]
image/x-ms-bmp	Windows OS/2 Bitmap Graphics [BMP]
image/x-wsq	Wavelet Scalar Quantization (WSQ) [WSQ]

B.3 Video Formats

Refer to [CMediaType] for more information regarding a registered video type.

multipart/x-mixed-replace	multipart/x-mixed-replace [HTML5] (§12.2)
video/h264	H.264 Video Compression [H264]
video/mpeg	Moving Pictures Experts Group [MPEG]
video/quicktime	QuickTime File Format [QTFF]
video/x-avi	Audio Video Interleave [AVI]
video/x-ms-asf	Advanced Systems Format [ASF]
video/x-ms-asx	Advanced Stream Redirector [ASX]
video/x-ms-wmv	Windows Media Video [ASF]

B.4 Audio Formats

Refer to [CMediaType] for more information regarding a registered audio type.

audio/3gpp	3rd Generation Partnership Project Multimedia files [3GPP]
audio/3gpp2	3rd Generation Partnership Project Multimedia files [3GPP2]
audio/mpeg	Moving Pictures Experts Group [MPEG1]
audio/ogg	Vorbis OGG Audio File [OGG]
audio/x-aiff	Audio Interchange File Format [AIFF]
audio/x-ms-wav	Waveform Audio File Format [WAVE]
audio/x-ms-wma	Windows Media Audio [ASF]
audio/x-sphere	NIST Speech Header Resources [SPHERE]

B.5 General Biometric Formats

x-biometric/x-ansi-nist-itl-2000	Information Technology: American National Standard for Information Systems—Data Format for the Interchange of Fingerprint, Facial, & Scar Mark & Tattoo (SMT) Information [AN2K]
x-biometric/x-ansi-nist-itl-2007	Information Technology: American National Standard for Information Systems—Data Format for the Interchange of Fingerprint, Facial, & Other Biometric Information – Part 1 [AN2K7]
x-biometric/x-ansi-nist-itl-2008	Information Technology: American National Standard for Information Systems—Data Format for the Interchange of Fingerprint, Facial, & Other Biometric Information – Part 2: XML Version [AN2K8]
x-biometric/x-ansi-nist-itl-2011	Information Technology: American National Standard for Information Systems—Data Format for the Interchange of Fingerprint, Facial & Other Biometric Information [AN2K11]
x-biometric/x-cbeff-2010	Common Biometric Exchange Formats Framework with Support for Additional Elements [CBEFF2010]

B.6 ISO / Modality-Specific Formats

x-biometric/x-iso-19794-2-05	Finger Minutiae Data [BDIF205]
x-biometric/x-iso-19794-3-06	Finger Pattern Spectral Data [BDIF306]
x-biometric/x-iso-19794-4-05	Finger Image Data [BDIF405]
x-biometric/x-iso-19794-5-05	Face Image Data [BDIF505]
x-biometric/x-iso-19794-6-05	Iris Image Data [BDIF605]
x-biometric/x-iso-19794-7-07	Signature/Sign Time Series Data [BDIF707]
x-biometric/x-iso-19794-8-06	Finger Pattern Skeletal Data [BDIF806]
x-biometric/x-iso-19794-9-07	Vascular Image Data [BDIF907]
x-biometric/x-iso-19794-10-07	Hand Geometry Silhouette Data [BDIF1007]

Appendix C. XML Schema

<?xml version="1.0"?>

<xs:schema xmlns:wsbd="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0"

xmlns:xs="http://www.w3.org/2001/XMLSchema"

targetNamespace="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0"

elementFormDefault="qualified">

<xs:element name="configuration" type="wsbd:Dictionary" nillable="true"/>

<xs:element name="result" type="wsbd:Result" nillable="true"/>

<xs:complexType name="Result">

<xs:sequence>

<xs:element name="status" type="wsbd:Status"/>

<xs:element name="badFields" type="wsbd:StringArray" nillable="true" minOccurs="0"/>

<xs:element name="captureIds" type="wsbd:UuidArray" nillable="true" minOccurs="0"/>

<xs:element name="metadata" type="wsbd:Dictionary" nillable="true" minOccurs="0"/>

<xs:element name="message" type="xs:string" nillable="true" minOccurs="0"/>

<xs:element name="sensorData" type="xs:base64Binary" nillable="true" minOccurs="0"/>

<xs:element name="sessionId" type="wsbd:UUID" nillable="true" minOccurs="0"/>

</xs:sequence>

</xs:complexType>

<xs:simpleType name="UUID">

<xs:restriction base="xs:string">

<xs:pattern value="[\da-fA-F]{8}-[\da-fA-F]{4}-[\da-fA-F]{4}-[\da-fA-F]{4}-[\da-fA-F]{12}"/>

</xs:restriction>

</xs:simpleType>

<xs:simpleType name="Status">

<xs:restriction base="xs:string">

<xs:enumeration value="success"/>

<xs:enumeration value="failure"/>

<xs:enumeration value="invalidId"/>

<xs:enumeration value="canceled"/>

<xs:enumeration value="canceledWithSensorFailure"/>

<xs:enumeration value="sensorFailure"/>

<xs:enumeration value="lockNotHeld"/>

<xs:enumeration value="lockHeldByAnother"/>

<xs:enumeration value="initializationNeeded"/>

<xs:enumeration value="configurationNeeded"/>

<xs:enumeration value="sensorBusy"/>

<xs:enumeration value="sensorTimeout"/>

<xs:enumeration value="unsupported"/>

<xs:enumeration value="badValue"/>

<xs:enumeration value="noSuchParamter"/>

<xs:enumeration value="preparingDownload"/>

</xs:restriction>

</xs:simpleType>

<xs:complexType name="Array">

<xs:sequence>

<xs:element name="element" type="xs:anyType" nillable="true" minOccurs="0" maxOccurs="unbounded"/>

</xs:sequence>

</xs:complexType>

<xs:complexType name="StringArray">

<xs:sequence>

<xs:element name="element" type="xs:string" nillable="true" minOccurs="0" maxOccurs="unbounded"/>

</xs:sequence>

</xs:complexType>

<xs:complexType name="UuidArray">

<xs:sequence>

<xs:element name="element" type="wsbd:UUID" nillable="true" minOccurs="0" maxOccurs="unbounded"/>

</xs:sequence>

</xs:complexType>

<xs:complexType name="Dictionary">

<xs:sequence>

<xs:element name="item" minOccurs="0" maxOccurs="unbounded">

<xs:complexType>

<xs:sequence>

<xs:element name="key" type="xs:string" nillable="true"/>

<xs:element name="value" type="xs:anyType" nillable="true"/>

</xs:sequence>

</xs:complexType>

</xs:element>

</xs:sequence>

</xs:complexType>

<xs:complexType name="Parameter">

<xs:sequence>

<xs:element name="name" type="xs:string" nillable="true"/>

<xs:element name="type" type="xs:QName" nillable="true"/>

<xs:element name="readOnly" type="xs:boolean" minOccurs="0"/>

<xs:element name="supportsMultiple" type="xs:boolean" minOccurs="0"/>

<xs:element name="defaultValue" type="xs:anyType" nillable="true"/>

<xs:element name="allowedValues" nillable="true" minOccurs="0">

<xs:complexType>

<xs:sequence>

<xs:element name="allowedValue" type="xs:anyType" nillable="true" minOccurs="0" maxOccurs="unbounded"/>

</xs:sequence>

</xs:complexType>

</xs:element>

</xs:sequence>

</xs:complexType>

<xs:complexType name="Range">

<xs:sequence>

<xs:element name="minimum" type="xs:anyType" nillable="true" minOccurs="0"/>

<xs:element name="maximum" type="xs:anyType" nillable="true" minOccurs="0"/>

<xs:element name="minimumIsExclusive" type="xs:boolean" nillable="true" minOccurs="0"/>

<xs:element name="maximumIsExclusive" type="xs:boolean" nillable="true" minOccurs="0"/>

</xs:sequence>

</xs:complexType>

<xs:complexType name="Resolution">

<xs:sequence>

<xs:element name="width" type="xs:double"/>

<xs:element name="height" type="xs:double"/>

<xs:element name="unit" type="xs:string" nillable="true" minOccurs="0"/>

</xs:sequence>

</xs:complexType>

</xs:schema >

Appendix D. Security (Informative)

This section is an informative appendix that provides security control recommendations for systems that include the use of WS-Biometric Devices.

Security requirements are context and organizational dependent. However, by providing general guidance, the OASIS Biometrics TC hopes to provide a common baseline that can be used to help ensure interoperability among components that leverage WS-Biometric Devices. If the approach to security varies widely among WS-BD enabled components, there is significantly less chance that off-the-shelf products will interoperate. This appendix is not a comprehensive security standard,—therefore, updates to security guidance incorporated by reference should take precedence to any recommendation made here. In addition, security recommendations tend to be continuously updated, evolved, and improved; always seek the latest version of any of the referenced security specifications.

Further, the security controls described here are specific to the WS-Biometric Devices protocols and the components using it. It is assumed controls described here are only one component of an implementation’s overall security.

D.1 References

The following references are used in this Appendix and can provide more specific security guidance for the identified technology.

Abbreviation	Technology	Citation
[802.1x]	Port-based network access control	*IEEE Standard 801.1X-2004, Institute of Electrical and Electronics Engineers, Standard for Local and metropolitan area networks, Port-Based Network Access Control, 2004.*
[FIPS 197]	Advanced encryption standard	*Federal Information Process Standards Publication 197. Advanced Encryption Standard (AES). November 2001.*
[OSI]	Network abstraction layers	*ISO/IEC 74989-1:1994(E). Open Systems Interconnect—Basic Reference Model: The Basic Model.*
[800-38A]	Block cipher modes of operation	*M. Dworkin. Recommendation for Block Cipher Modes of Operation: Methods and Techniques. NIST Special Publication 800-38A. December 2001.*
[SP 800-60]	System sensitivity classifications	*K. Stine, et al. Guide for Mapping Types of Information and Information Systems to Security Categories. NIST Special Publication 800-600, Volume 1, Revision 1. August 2008.*
[SP 800-52]	Transport Layer Security (TLS)	T. Polk, S. Chokhani, and K. McKay. DRAFT Guidelines for the Selection, Configuration, and Use of Transport Layer Security (TLS) Implementations. NIST Special Publication 800-52 Revision 1. September 2013.
[SP 800-77]	IPSEC	*S. Frankel, K. Kent, R. Lewkowski, A. Orebaugh, R. Ritchey, S. Sharma. Guide to IPsec VPNs. NIST Special Publication 800-77. December 2005.*
[SP 800-97]	Wireless network security	*S. Frankel, B. Eydt, L. Owens, K. Scarfone. Establishing Wireless Robust Security Networks, A Guide to IEEE 802.11i. NIST Special Publication 800-97. February 2007.*
[SP 800-113]	SSL VPN	*S. Frankel, P. Hoffman, A. Orebaugh, R. Park. Guide to SSL VPNs. NIST Special Publication 800-113. July 2008.*

D.2 Overview

WS-Biometric Devices components are only useful in the context of the system within which they participate. Therefore, recommended security controls are defined with respect to two orthogonal characteristics of those enclosing systems:

1. An overall sensitivity level of low (L), medium (M), or high (H) defines a set of recommended security controls. These levels roughly, but not directly, correspond to those defined in [NIST SP 800-60]. The 800-60 level accompanies other information as inputs for determining the set of recommended controls specific for WS-BD. For the sake of disambiguation, “L,” “M,” or “H” will refer to a set of controls recommended by this appendix.

2. For each sensitivity level, a set of controls is recommended to be applied at a particular layer of abstraction. For each sensitivity level, recommendations are made for controls to be applied at the network, transport and/or application level. These levels roughly, but not directly, correspond to the network, transport, and application layers defined in the OSI model [OSI].

D.3 Control Set Determination

The following criteria are recommended for helping users and system owners in identifying a recommended set of security controls.

D.3.1 “L” Security Control Criteria

The set of “L” controls are recommended if, for a given system, each of the following three clauses are true:

1. The system is used in a non-production environment or has an overall NIST SP 800-60 sensitivity of “Low”

2. All WS-Biometric Devices clients and servers reside within the same trusted network

3. The network that provides the WS-Biometric Devices interconnectivity network is completely isolated or otherwise security separated from untrusted networks with a strong buffer such as a comprehensive network firewall.

Examples that may qualify for “L” security controls are the use of WS-Biometric devices:

· In product development, testing, or other research where no real biometric data is stored or captured

· Across physical or logical components that are within an embedded device with other physical or logical controls that make it difficult to access or surreptitiously monitor the channels that carry WS-Biometric Devices traffic.

D.3.2 “M” Security Control Criteria

The set of “M” controls are recommended if, for a given system, each of the following three clauses are true:

1. The system is used in a production environment or the system has an overall NIST SP 800-60 sensitivity of “Medium”

2. All WS-Biometric Devices clients and servers reside within the same trusted network

3. The system’s network is either completely isolated or otherwise security separated from untrusted networks with a buffer such as a firewall.

Examples that may qualify for “M” security controls are the use of WS-Biometric devices:

· In an identification enrollment station, where WS-Biometric Devices is used as a “wire replacement” for other less interoperable connectors. The WS-Biometric Devices network could be composed solely of the enrollment workstation and a biometric device with an Ethernet cable between them.

· In a border screening application in which attended workstations in physically secure locations are used to submit biometrics to various law enforcement watch lists.

D.3.3 “H” Security Control Criteria

The set of “H” controls are recommended if the overall system has an NIST SP 800-60 sensitivity of “High” or if WS-Biometric Devices is used across an untrusted network.

The following table outlines the candidate & recommended security controls. Recommended security controls are likely to be relevant and beneficial for all systems of a particular category. Candidate controls are those that are likely to more application and implementation specific.

Candidate controls are marked with an asterisk (*). For example, in all “L” systems, any wireless networking should use WPA-2 Personal with 256-bit strength encryption (or better), and is therefore recommended. However, the use of TLS is a candidate since an “L” system might comprise a communications channel that is physically isolated or otherwise embedded in a system. In that case, foregoing TLS may be an acceptable tradeoff.

There may be a degree of redundancy among these controls; for example, multiple layers of encryption. However, using multiple layers of security also affords more granular policy enforcement. For example, IPSEC may allow the communications among one set of systems, but TLS client certificates would restrict WS-Biometric Devices communications to a particularly trustworthy subset..

		L	M	H
Network Layer	Wired	None	802.1x and/or IPSEC*	IPSEC
Network Layer	Wireless	WPA-2 Personal	WPA-2 Enterprise	WPA-2 Enterprise
Transport Layer		TLS [SP 800-52]	TLS [SP 800-52]	TLS with client certificates [SP 800-52]
Application Layer		None	Biometric payload encryption with AES*	Full payload encryption with AES

D.4.1 “L” Security Controls

Network. No network security controls are recommended for wired networks. For wireless networks, WPA-2, personal or enterprise mode is recommended.

Transport. TLS as described in [800-52]; the use of client certificates is optional.

Application. No application layer security control is recommended.

D.4.2 “M” Security Controls

Network. Networks should be secured with 802.1x [802.1x] and/or IPSEC [SP 800-77].

Transport. TLS as described in [800-52]; the use of client certificates is optional.

Application. All biometric data (the contents of a Result’s sensorData) should be encrypted with AES as described in [FIPS 197] and [SP 800-38A].

D.4.3 “H” Security Controls

Network. Networks should be secured with an IPSEC [800-77].

Transport. TLS with client certificates as described in [800-52].

Application. All biometric data (the contents of a Result’s sensorData) should be encrypted with AES as described in [FIPS 197] and [SP 800-38A].

Appendix E. Acknowledgments

The following individuals have participated in the creation of this specification and are gratefully acknowledged:

Participants:

Almog Aley-Raz, Nuance

Mr. Jeremiah Bruce, US Department of Homeland Security

Mr. Doron Cohen, SafeNet, Inc.

Robin Cover, OASIS

Matthias de Haan, Tandent Vision Science, Inc

Mr. Francisco Diez-Jimeno, Carlos III University of Madrid

Dr. Jeff Dunne, Johns Hopkins University Applied Physics Laboratory

Mr. Chet Ensign, OASIS

Mr. Sander Fieten, Individual

Richard Friedhoff, Tandent Vision Science, Inc

Bob Gupta, Viometric, LLC

Emily Jay, NIST

Mr. Ken Kamakura, Fujitsu Limited

Mr. Kevin Mangold, NIST

Dr. Ross Micheals, NIST

Derek Northrope, Fujitsu Limited

Mr Tony Pham, Bank of America

Dr. Raul Sanchez-Reillo, Carlos III University of Madrid

Mrs. Dee Schur, OASIS

Mr. Jeffrey Shultz, US Department of Defense (DoD)

Casey Smith, Tandent Vision Science, Inc

Mr. Kevin Strickland, Tandent Vision Science, Inc

Cathy Tilton, Daon

Mr. Ryan Triplett, Booz Allen Hamilton

Ms. Maria Vachino, Johns Hopkins University Applied Physics Laboratory

Mr. Steven Venable, Lockheed Martin

Anne Wang, 3M HIS

Youngrock Yoon, Tandent Vision Science, Inc

Authors of initial NIST specification

Ross J. Micheals

Kevin Mangold

Matt Aronoff

Kristen Greene

Kayee Kwong

Karen Marshall

Acknowledgments listed in initial NIST specification

The authors thank the following individuals and organizations for their participation in the creation of this specification.

Biometric Standards Working Group, Department of Defense

Michael Albright, Vision and Security Technology Laboratory, University of Colorado at Colorado Springs

Senaka Balasuriya, SolidBase Consulting

Terrance Boult, Vision and Security Technology Laboratory, University of Colorado at Colorado Springs

Leslie Collica, Information Technology Laboratory, National Institute of Standards and Technology

Tod Companion, Science & Technology Directorate, Department of Homeland Security

Bert Coursey, Science & Technology Directorate, Department of Homeland Security

Nick Crawford, Government Printing Office

Donna Dodson, Information Technology Laboratory, National Institute of Standards and Technology

Valerie Evanoff, Biometric Center of Excellence, Federal Bureau of Investigation

Rhonda Farrell, Booz Allen Hamilton

Michael Garris, Information Technology Laboratory, National Institute of Standards and Technology

Phillip Griffin, Booz Allen Hamilton

Dwayne Hill, Biometric Standards Working Group, Department of Defense

Rick Lazarick, Computer Sciences Corporation

John Manzo, Biometric Center of Excellence, Federal Bureau of Investigation

Charles Romine, Information Technology Laboratory, National Institute of Standards and Technology

James St. Pierre, Information Technology Laboratory, National Institute of Standards and Technology

Scott Swann, Federal Bureau of Investigation

Ashit Talukder, Information Technology Laboratory, National Institute of Standards and Technology

Cathy Tilton, Daon Inc.

Ryan Triplett, Biometric Standards Working Group, Department of Defense

Bradford Wing, Information Technology Laboratory, National Institute of Standards and Technology

Appendix F. Revision History

Revision	Date	Editor(s)	Changes Made
Working Draft 01	26 March 2013	Ross Micheals	Initial working draft based on NIST specification
Working Draft 02	06 September 2013	Kevin Mangold, Ross Micheals	Incorporated methods of exposing a live preview endpoint(s). Updated schema namespace.
Working Draft 03	04 March 2014	Kevin Mangold, Ross Micheals	Draft implementation of conformance profiles and security guidance
Working Draft 04	02 April 2014	Ross Micheals	Completed security guidance appendix.
Working Draft 05	July 2014	Ross Micheals, Kevin Mangold	Harmonized security guidance and appendix; updated security appendix to reflect updated NIST Special Publication
Working Draft 06	August 2014	Ross Micheals	Completed basic conformance profiles, preparing manuscript for consideration by the TC as a Committee Specification Draft. Corrected minor typos and made minor cosmetic fixes.