WS-Biometric Devices Version 1.0

Committee Specification Draft 02 /
Public Review Draft 02

12 November 2014

Specification URIs

This version:

http://docs.oasis-open.org/biometrics/WS-BD/v1.0/csprd02/WS-BD-v1.0-csprd02.pdf (Authoritative)

http://docs.oasis-open.org/biometrics/WS-BD/v1.0/csprd02/WS-BD-v1.0-csprd02.html

http://docs.oasis-open.org/biometrics/WS-BD/v1.0/csprd02/WS-BD-v1.0-csprd02.doc

Previous version:

http://docs.oasis-open.org/biometrics/WS-BD/v1.0/csprd01/WS-BD-v1.0-csprd01.doc (Authoritative)

http://docs.oasis-open.org/biometrics/WS-BD/v1.0/csprd01/WS-BD-v1.0-csprd01.html

http://docs.oasis-open.org/biometrics/WS-BD/v1.0/csprd01/WS-BD-v1.0-csprd01.pdf

Latest version:

http://docs.oasis-open.org/biometrics/WS-BD/v1.0/WS-BD-v1.0.pdf (Authoritative)

http://docs.oasis-open.org/biometrics/WS-BD/v1.0/WS-BD-v1.0.html

http://docs.oasis-open.org/biometrics/WS-BD/v1.0/WS-BD-v1.0.doc

Technical Committee:

OASIS Biometrics TC

Chair:

Kevin Mangold (kevin.mangold@nist.gov), NIST

Editors:

Kevin Mangold (kevin.mangold@nist.gov), NIST

Ross J. Micheals (ross.micheals@nist.gov), NIST

Additional artifacts:

This prose specification is one component of a Work Product that also includes:

·         XML schemas: http://docs.oasis-open.org/biometrics/WS-BD/v1.0/csprd02/schemas/

Related work:

This specification replaces or supersedes:

·         Specification for WS-Biometric Devices (WS-BD) Version 1. http://www.nist.gov/itl/iad/ig/upload/NIST-SP-500-288-v1.pdf

Declared XML namespaces:

·         http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0

Abstract:

WS-Biometric Devices is a protocol for the command and control of biometric sensors using the same protocols that underlie the Web.

Status:

This document was last revised or approved by the OASIS Biometrics TC on the above date. The level of approval is also listed above. Check the “Latest version” location noted above for possible later revisions of this document. Any other numbered Versions and other technical work produced by the Technical Committee (TC) are listed at https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=biometrics#technical.

TC members should send comments on this specification to the TC’s email list. Others should send comments to the TC’s public comment list, after subscribing to it by following the instructions at the “Send A Comment” button on the TC’s web page at https://www.oasis-open.org/committees/biometrics/.

For information on whether any patents have been disclosed that may be essential to implementing this specification, and any offers of patent licensing terms, please refer to the Intellectual Property Rights section of the Technical Committee web page (https://www.oasis-open.org/committees/biometrics/ipr.php).

Citation format:

When referencing this specification the following citation format should be used:

[WS-BD-v1.0]

WS-Biometric Devices Version 1.0. Edited by Kevin Mangold and Ross J. Micheals. 12 November 2014. OASIS Committee Specification Draft 02 / Public Review Draft 02. http://docs.oasis-open.org/biometrics/WS-BD/v1.0/csprd02/WS-BD-v1.0-csprd02.html. Latest version: http://docs.oasis-open.org/biometrics/WS-BD/v1.0/WS-BD-v1.0.html.

Notices

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Table of Contents

1        Introduction. 10

1.1 Motivation. 10

1.2 Terminology. 10

1.3 Documentation Conventions. 11

1.3.1 About 11

1.3.2 Key Words. 11

1.3.3 Quotations. 11

1.3.4 Machine-Readable Code. 12

1.3.5 Sequence Diagrams. 12

1.4 References. 13

2        Design Concepts and Architecture. 17

2.1 About 17

2.2 Interoperability. 17

2.3 Architectural Components. 17

2.3.1 Overview. 17

2.3.2 Client 17

2.3.3 Sensor 18

2.3.4 Sensor Service. 18

2.4 Intended Use. 18

2.5 General Service Behavior 19

2.5.1 About 19

2.5.2 Security Model 19

2.5.3 HTTP Request-Response Usage. 19

2.5.4 Client Identity. 20

2.5.5 Sensor Identity. 21

2.5.6 Locking. 22

2.5.7 Operations Summary. 23

2.5.8 Idempotency. 24

2.5.9 Service Lifecycle Behavior 24

3        Data Dictionary. 26

3.1 About 26

3.2 Namespaces. 26

3.3 UUID.. 26

3.4 Dictionary. 27

3.5 Parameter 27

3.5.1 Overview. 27

3.5.2 Element Summary. 28

3.6 Range. 30

3.7 Array. 30

3.8 StringArray. 31

3.9 UuidArray. 31

3.10 ResourceArray. 31

3.11 Resource. 32

3.12 Resolution. 32

3.13 Status. 32

3.14 Result 34

3.14.1 Overview. 34

3.14.2 Terminology Shorthand. 35

3.14.3 Required Elements. 35

3.14.4 Element Summary. 35

3.15 Validation. 36

4        Metadata. 37

4.1 About 37

4.2 Service Information. 37

4.3 Configuration. 38

4.4 Captured Data. 38

4.4.1 Overview. 38

4.4.2 Minimal Metadata. 39

5        Live Preview. 41

5.1 About 41

5.2 Endpoints. 41

5.3 Heartbeat 42

6        Operations. 44

6.1 About 44

6.2 General Usage. 44

6.2.1 Overview. 44

6.2.2 Precedence of Status Enumerations. 44

6.2.3 Parameter Failures. 46

6.2.4 Visual Summaries (Informative) 46

6.3 Documentation Conventions. 48

6.3.1 About 48

6.3.2 General Information. 48

6.3.3 Result Summary. 49

6.3.4 Usage. 50

6.3.5 Unique Knowledge. 50

6.3.6 Return Values Detail 50

6.4 Register 51

6.4.1 Overview. 51

6.4.2 Result Summary. 51

6.4.3 Usage. 51

6.4.4 Unique Knowledge. 51

6.4.5 Return Values Detail 51

6.5 Unregister 53

6.5.1 Overview. 53

6.5.2 Result Summary. 53

6.5.3 Usage. 53

6.5.4 Unique Knowledge. 54

6.5.5 Return Values Detail 54

6.6 Try Lock. 56

6.6.1 Overview. 56

6.6.2 Result Summary. 56

6.6.3 Usage. 56

6.6.4 Unique Knowledge. 56

6.6.5 Return Values Detail 56

6.7 Steal Lock. 59

6.7.1 Overview. 59

6.7.2 Result Summary. 59

6.7.3 Usage. 59

6.7.4 Unique Knowledge. 60

6.7.5 Return Values Detail 60

6.8 Unlock. 62

6.8.1 Overview. 62

6.8.2 Result Summary. 62

6.8.3 Usage. 62

6.8.4 Unique Knowledge. 62

6.8.5 Return Values Detail 62

6.9 Get Service Info. 64

6.9.1 Overview. 64

6.9.2 Result Summary. 64

6.9.3 Usage. 64

6.9.4 Unique Knowledge. 66

6.9.5 Return Values Detail 66

6.10 Initialize. 67

6.10.1 Overview. 67

6.10.2 Result Summary. 67

6.10.3 Usage. 67

6.10.4 Unique Knowledge. 68

6.10.5 Return Values Detail 68

6.11 Get Configuration. 71

6.11.1 Overview. 71

6.11.2 Result Summary. 71

6.11.3 Usage. 71

6.11.4 Unique Knowledge. 72

6.11.5 Return Values Detail 72

6.12 Set Configuration. 77

6.12.1 Overview. 77

6.12.2 Result Summary. 77

6.12.3 Usage. 78

6.12.4 Unique Knowledge. 78

6.12.5 Return Values Detail 78

6.13 Capture. 84

6.13.1 Overview. 84

6.13.2 Result Summary. 84

6.13.3 Usage. 84

6.13.4 Unique Knowledge. 85

6.13.5 Return Values Detail 85

6.14 Download. 90

6.14.1 Overview. 90

6.14.2 Result Summary. 90

6.14.3 Usage. 90

6.14.4 Unique Knowledge. 94

6.14.5 Return Values Detail 94

6.15 Get Download Info. 96

6.15.1 Overview. 96

6.15.2 Result Summary. 96

6.15.3 Usage. 96

6.15.4 Unique Knowledge. 96

6.15.5 Return Values Detail 96

6.16 Thrifty Download. 99

6.16.1 Overview. 99

6.16.2 Result Summary. 99

6.16.3 Usage. 99

6.16.4 Unique Knowledge. 100

6.16.5 Return Values Detail 100

6.17 Cancel 103

6.17.1 Overview. 103

6.17.2 Result Summary. 103

6.17.3 Usage. 103

6.17.4 Unique Knowledge. 105

6.17.5 Return Values Detail 105

7        Conformance Profiles. 107

7.1 About 107

7.2 Conformance Requirements. 107

7.3 Claims of Conformance. 107

7.4 Language. 107

7.5 Operations & Conformance Levels. 108

7.6 Fingerprint Service Information. 109

7.6.1 Submodality. 109

7.6.2 Image Size. 109

7.6.3 Image Content Type. 110

7.6.4 Image Density. 110

7.7 Face Service Information. 110

7.7.1 Submodality. 110

7.7.2 Image Size. 110

7.7.3 Image Content Type. 111

7.8 Iris Service Information. 111

7.8.1 Submodality. 111

7.8.2 Image Size. 111

7.8.3 Image Content Type. 112

Appendix A.       Parameter Details (Normative) 113

A.1 About 113

A.2 Connection Parameters. 113

A.2.1 Last Updated. 113

A.2.2 Inactivity Timeout 113

A.2.3 Maximum Concurrent Sessions. 113

A.2.4 Least Recently Used (LRU) Sessions Automatically Dropped. 114

A.3 Timeout Parameters. 114

A.3.1 About 114

A.3.2 Initialization Timeout 114

A.3.3 Get Configuration Timeout 114

A.3.4 Set Configuration Timeout 115

A.3.5 Capture Timeout 115

A.3.6 Post-Acquisition Processing Time. 115

A.3.7 Lock Stealing Prevention Period. 115

A.4 Storage Parameters. 116

A.4.1 About 116

A.4.2 Maximum Storage Capacity. 116

A.4.3 Least-Recently Used Capture Data Automatically Dropped. 116

A.5 Sensor Parameters. 116

A.5.1 Modality. 116

A.5.2 Submodality. 117

Appendix B.       Content Type Data (Normative) 118

B.1 About 118

B.2 General Type. 118

B.3 Image Formats. 118

B.4 Video Formats. 118

B.5 Audio Formats. 118

B.6 General Biometric Formats. 119

B.7 ISO / Modality-Specific Formats. 119

Appendix C.       XML Schema (Informative) 120

Appendix D.       Security (Informative) 122

D.1 About 122

D.2 References. 122

D.3 Overview. 123

D.4 Control Set Determination. 123

D.4.1 “L” Security Controls Criteria. 123

D.4.2 “M” Security Controls Criteria. 123

D.4.3 “H” Security Controls Criteria. 124

D.5 Recommended & Candidate Security Controls. 124

D.5.1 “L” Security Controls. 124

D.5.2 “M” Security Controls. 125

D.5.3 “H” Security Controls. 125

Appendix E.       Acknowledgments (Informative) 126

Appendix F.        Revision History (Informative) 128

 

 


1      Introduction

1.1 Motivation

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.

1.2 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 [RFC-HTTP] 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

sensor service

a “middleware” software component that exposes a biometric sensor to a client through web services

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]

1.3 Documentation Conventions

1.3.1 About

This section (§1.3) describes the style and usage conventions used throughout this document.

1.3.2 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].

1.3.3 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”.

1.3.4 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.

1.3.5 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.

Figure 1 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 (§6.4 through §6.17) 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 (§3.14.2). 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 (§2.5.4, §3.14.4, §6.4); “{C1D10123...}” and “{D2E21234...}” represent capture ids (§3.14.4, §6.13).

 

1.4 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 , R. Berjon, S. Faulkner, T. Leithead, E. Doyle Navara, E. O'Connor, S. Pfeiffer, Editors, W3C (work in progress), 16 September 2014, http://www.w3.org/TR/2014/PR-html5-20140916/. Latest version available at http://www.w3.org/TR/html5/

[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]

Portable Network Graphics (PNG) Specification (Second Edition) , D. Duce, Editor, W3C, 10 November 2003, http://www.w3.org/TR/2003/REC-PNG-20031110. Latest version available at http://www.w3.org/TR/PNG

[QTFF]

Introduction to Quicktime File Format Specification, https://developer.apple.com/library/mac/documentation/QuickTime/QTFF/QTFFPreface/qtffPreface.html, Retrieved 12 August 2014

[RFC1737]

Sollins, K. and L. Masinter, "Functional Requirements for Uniform Resource Names", RFC 1737, December 1994, http://www.rfc-editor.org/info/rfc1737.

[RFC2045]

Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996, http://www.rfc-editor.org/info/rfc2045.

[RFC2046]

Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996, http://www.rfc-editor.org/info/rfc2046.

[RFC2119]

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997, http://www.rfc-editor.org/info/rfc2119.

[RFC2141]

Moats, R., "URN Syntax", RFC 2141, May 1997, http://www.rfc-editor.org/info/rfc2141.

[RFC-HTTP]

Fielding, R., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, June 2014, http://www.rfc-editor.org/info/rfc7230.

Fielding, R., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, June 2014, http://www.rfc-editor.org/info/rfc7231.

Fielding, R., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests", RFC 7232, June 2014, http://www.rfc-editor.org/info/rfc7232.

Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Range Requests", RFC 7233, June 2014, http://www.rfc-editor.org/info/rfc7233.

Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", RFC 7234, June 2014, http://www.rfc-editor.org/info/rfc7234.

[RFC2660]

Rescorla, E. and A. Schiffman, "The Secure HyperText Transfer Protocol", RFC 2660, August 1999, http://www.rfc-editor.org/info/rfc2660.

[RFC3061]

Mealling, M., "A URN Namespace of Object Identifiers", RFC 3061, February 2001, http://www.rfc-editor.org/info/rfc3061.

[RFC4122]

Leach, P., Mealling, M., and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, July 2005, http://www.rfc-editor.org/info/rfc4122.

[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]

Extensible Markup Language (XML) 1.0 (Fifth Edition) , T. Bray, J. Paoli, M., E. Maler, F. Yergeau, Editors, W3C, 26 November 2008, http://www.w3.org/TR/2008/REC-xml-20081126/. Latest version available at http://www.w3.org/TR/xml .

[XML-NAMES]

Namespaces in XML 1.0 (Third Edition) , T. Bray, D. Hollander, A. Layman, R. Tobin, H. S. Thompson, Editors, W3C , 8 December 2009, http://www.w3.org/TR/2009/REC-xml-names-20091208/. Latest version available at http://www.w3.org/TR/xml-names

[XMSCHEMA-1]

XML Schema Part 1: Structures Second Edition, H. S. Thompson, D. Beech, M. Maloney, N. Mendelsohn, Editors, W3C, 28 October 2004, http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/  Latest version available at http://www.w3.org/TR/xmlschema-1/ .

[XMSCHEMA-2]

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

2.1 About

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.

2.2 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 technical committee recognizes 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.

2.3 Architectural Components

2.3.1 Overview

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.

2.3.2 Client

A client is any software component that originates WS-BD operation requests. A client can be one of many hosted in a parent (logical or physical) component, and that a client can 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.

 

2.3.3 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 can 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.

2.3.4 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.

2.4 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.

 

___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.

__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 can 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 §2.3.3 practitioners may need to clearly define appropriate logical and physical boundaries for their own context of use.

2.5 General Service Behavior

2.5.1 About

This section (§2.5) describes the general behavior of WS-BD clients and services.

2.5.2 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.

2.5.3 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 200–299 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 1 (Informative): 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 technical commitee 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 technical committee 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.

2.5.4 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 §6.5.3.2).

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 may opt to create a single session for its entire lifetime, or, may 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 may maintain multiple session ids, a single session id may 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.

2.5.5 Sensor Identity

A WS-BD service must be exposed to potential clients by a unique URI that serves as entry point for that service.

Implementers should map each target biometric sensor to a single service; that is, independent sensors should be exposed via different URIs. However, just as it is possible for a client to communicate with multiple services, a host can be responsible for controlling multiple target biometric sensors.


Example 1:  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; this SHOULD NOT be the preferred architecture if the sensors would need to be addressed or controlled separately.

Figure 5. A sensor array controlled by a single service.


Example 2: 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. The left and right camera are not individually addressable because the service is exposing both by a single endpoint. If the left and right camera needed to be separately addressable, then the host should expose two services—one for each camera—http://wsbd/left_camera and http://wsbd/right_camera.


A biometric sensor should not be exposed by more than one service at a time as it can significantly increase the complexity of implementation.

2.5.6 Locking

2.5.6.1 Overview and General Behavior

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 sequence of sensor operations and not be interrupted by another client

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. There must only be a single lock per service—regardless of the number of underlying biometric sensors under the service’s control. (This is one of the reasons why implementers should map each target biometric sensor to a single endpoint.)

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 may obtain and release the lock many times within the same session or a client may 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 may “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 §2.5.4), 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 2 (Informative): In the early development states of this specification, the specification designers 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.

WS-BD only offers the core locking, unlocking, and lock stealing operations. Any other lock coordination is outside of scope of this specification and is the clients’ responsibility.

2.5.6.2 Pending Operations

Changing the state of the lock must have no effect on pending (i.e., currently running) sensor operations. That is, a service must not interrupt ongoing sensor operations even if a client unlocks, steals, or re-obtains a service lock. In this case, overlapping sensor operations are prevented by sensor operations returning sensorBusy.

2.5.7 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 could 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.

2.5.8 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 3: 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 4: 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.

2.5.9 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.

Consequently, this specification does NOT make any specific recommendations on how a WS-BD service should be started, stopped, or reset. This (a) reflects the connectionless nature of HTTP but also (b) allows the host environment maximum flexibility on how to implement service availability. For example, a manufacturer of an embedded device might elect to have the device run a service as long as the device is powered on.

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.

If the service is written in a robust manner, then a client SHOULD NOT be directly affected by a service restart, For example, upon detecting a new target biometric sensor, a robust server could quiesce (refuse all new requests until 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.2.1) to detect potential changes in the get service info operation.

3      Data Dictionary

3.1 About

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 [XMSCHEMA-1, XMSCHEMA-2].

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

important: XML Schema (and fragments) are used throughout this section and this document for the convenience of the reader so that the document may be self-contained. However, in the event that there is a discrepancy between this document and the electronic version of the schema that accompanies this specification, the electronic version shall be the authoritative source.

3.2 Namespaces

Table 1 lists the namespaces and corresponding namespace prefixes are used throughout this document.

Table 1. Namespaces

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 [XMSCHEMA-2].

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 [RFC3061] 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.

3.3 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 5: Each of the following is a well-formed UUID.

E47991C3-CA4F-406A-8167-53121C0237BA              

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

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


3.4 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 6: 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>

  <value>640</value>

</item>

<item>

  <key>imageHeight</key>

  <value>640</value>

</item>

<item>

  <key>captureDate</key>

  <value>2011-01-01T01:23:45Z</value>

</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 [XMSCHEMA-1, XMSCHEMA-2] 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.

3.5 Parameter

3.5.1 Overview

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.

3.5.2 Element Summary

Table 2 contains a description of each Parameter element.

Table 2. Parameter—element summary

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 (§3.5.2.1).

defaultValue

The default value of this parameter.

allowedValues

A list of allowed values for this parameter (§3.5.2.2).

3.5.2.1 “Supports Multiple” Element

In some cases, a parameter MAY 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 (§3.8) for xs:string, such type should be used. The generic Array (§3.7) 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 7: 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:

<name>submodality</name>

<type>xs:string</type>

<readOnly>false</readOnly>

<supportsMultiple>true</supportsMultiple>

<defaultValue xsi:type="wsbd:StringArray">

  <element>leftIris</element>

  <element>rightIris</element>

</defaultValue>

<allowedValues>

  <allowedValue>leftIris</allowedValue>

  <allowedValue>rightIris</allowedValue>

  <allowedValue>frontalFace</allowedValue>

</allowedValues>             

The second code block is how a client would configure this parameter for simultaneous left and right iris capture.

<item>

  <key>submodality</key>

  <value xsi:type="wsbd:StringArray">

    <element>leftIris</element>

    <element>rightIris</element>

  </value>

</item>

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.

The resulting captured data must specify the respective submodality for each captured item in its metadata.

In both code blocks, enclosing tags (which may vary) are omitted.


3.5.2.2 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 8: 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>

<defaultValue>auto</defaultValue>

<allowedValues>

  <allowedValue xsi:type="xs:string">on</allowedValue>

  <allowedValue xsi:type="xs:string">off</allowedValue>

  <allowedValue xsi:type="xs:string">auto</allowedValue>

</allowedValues>


Parameters requiring a range of values should be described by using Range (§3.6). 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 9: 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>

<defaultValue>0</defaultValue>

<allowedValues>

  <allowedValue xsi:type="wsbd:Range">

    <minimum>0</minimum>

    <maximum>100</maximum>

  </allowedValue>

</allowedValues>


If a configurable parameter has no restrictions on its value then the parameter must not include the allowedValues element.

3.6 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 10: 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.

  <minimum>0</minimum>

  <maximum>100</maximum>

  <minimumIsExclusive>true</minimumIsExclusive>

  <maximumIsExclusive>false</maximumIsExclusive>


Table 3 provides a description of each Range element.

Table 3. Range—element summary

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.

3.7 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 11: In the following fragment the values “flatLeftThumb” and “flatRightThumb” are of type xs:anyType, and are likely to be deserialized as a generic “object.”

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

Example 12: In the following  fragment, the two values are of different types.

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

Example 13: In the following fragment, the array contains a single element.

<element xsi:type="xs:decimal">2.0</element>


3.8 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 14: Each line below 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>


3.9 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 15: The following code fragment is an example of a single UuidArray with three elements. Enclosing tags (which may vary) are omitted.

<element>E47991C3-CA4F-406A-8167-53121C0237BA</element>

<element>10fa0553-9b59-4D9e-bbcd-8D209e8d6818</element>

<element>161FdBf5-047F-456a-8373-D5A410aE4595</element>


3.10 ResourceArray

A ResourceArray is a generic container used to hold a collection of Resources (§3.11).

<xs:complexType name="ResourceArray">

  <xs:sequence>

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

  </xs:sequence>

</xs:complexType>

 


EXAMPLE 16: 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>


3.11 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>

3.12 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>

Table 4 provides a description of each Size element.

Table 4. Resolution—element summary

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

3.13 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>

Table 5 defines all of the potential values for the Status enumeration.

Table 5. 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 (§6.5.3.2)

(See §6.2.3 for information on parameter failures.)

canceled

The operation was canceled.

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.

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 that prohibits the request.

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 §6.14.3.3 for information about post-acquisition processing.)

sensorTimeout

The operation was not performed because the biometric sensor experienced a timeout.

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 §6.2.3 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 §6.2.3 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 §6.2.3 for information on parameter failures.)

preparingDownload

The operation could not be performed because the service is currently preparing captured data for download. (See §6.14.3.3)

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 may be required.

3.14 Result

3.14.1 Overview

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>

3.14.2 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 17: 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.

3.14.3 Required Elements

Notice that from a XML Schema validation perspective [XMSCHEMA-1], 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 18: As will be detailed later (§6.4.5.2 and §6.6.5.2), 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 3 (Informative): 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.

3.14.4 Element Summary

Table 6 provides a brief description of each element of a Result.

Table 6. Result — element summary

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 (§6.13, §6.14).

metadata

This field may hold

a)     metadata for the service (§6.9), or

b)    a service and sensor’s configuration (§6.11, §6.12), or

c)     metadata relating to a particular capture (§6.14, §6.15, §6.16)

(See §4 for 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 (§6.14, §6.16).

sessionId

A unique session identifier (§6.4).

3.15 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. 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

4.1 About

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.

4.2 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 (§3.5).

Parameters listed in §A.2, §A.3, and §A.4 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 19: 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>

<readOnly>true</readOnly>

<supportsMultiple>false</supportsMultiple>

<defaultValue>600</defaultValue>


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 (§3.6).


Example 20: 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>

<defaultValue>800</defaultValue>

<allowedValues>

  <allowedValue>640</allowedValue>

  <allowedValue>800</allowedValue>

  <allowedValue>1024</allowedValue>

</allowedValues>


In many cases, an exposed parameter will support multiple values (see §3.5.2.1). When a parameter allows this capability, it must use a type-specific array, if defined in this specification, or the generic Array (§3.7) type. The type element within a parameter must be the qualified name of a single value’s type (see §3.5.2.1 for an example).

4.3 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 21: 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>

    <value xsi:type="xs:int">480</value>

  </item>

  <item>

    <key>imageWidth</key>

    <value xsi:type="xs:int">640</value>

  </item>

  <item>

    <key>frameRate</key>

    <value xsi:type="xs:int">20</value>

  </item>

</configuration>


4.4 Captured Data

4.4.1 Overview

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 22:  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>

  <value xsi:type="xs:string">98A8N830LP332-V244</value>

</item>

<item>

  <key>imageHeight</key>

  <value xsi:type="xs:string">600</value>

</item>

<item>

  <key>imageWidth</key>

  <value xsi:type="xs:string">800</value>

</item>

<item>

  <key>captureTime</key>

  <value xsi:type="xs:dateTime">2011-12-02T09:39:10.935-05:00</value>

</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 23:  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>

  <value>78</value>

</item>

<item>

  <key>serialNumber</key>

  <value>98A8N830LP332-V244</value>

</item>

<item>

  <key>captureDate</key>

  <value>2011-01-01T15:30:00Z</value>

</item>

<item>

  <key>modality</key>

  <value>Finger</value>

</item>

<item>

  <key>submodality</key>

  <value>leftIndex</value>

</item>

<item>

  <key>imageHeight</key>

  <value>600</value>

</item>

<item>

  <key>imageWidth</key>

  <value>800</value>

</item>

<item>

  <key>contentType</key>

  <value>image/bmp</value>

</item>


4.4.2 Minimal Metadata

4.4.2.1 General

At a minimum, a sensor or service must maintain the following (§4.4.2.2–§4.4.2.5) metadata fields for each captured result.

4.4.2.2 Capture Date

Formal Name

captureDate

Data Type

xs:dateTime [XMSCHEMA-2]

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

4.4.2.3 Modality

Formal Name

modality

Data Type

xs:string [XMSCHEMA-2]

The value of this field must be present in the list of available modalities exposed by the get service info operation (§6.9) as defined in §A.5.1. This value represents the modality of the captured result.

4.4.2.4 Submodality

Formal Name

submodality

Data Type

xs:anyType [XMSCHEMA-2]

The value of this field must be present in the list of available submodalities exposed by the get service info operation (§6.9) as defined in §A.5.2. This value represents the submodality of the captured result. If this parameter supports multiple, then the data type must be a StringArray (§3.8) of values. If submodality does not support multiple, the data type must be xs:string [XMSCHEMA-2].

4.4.2.5 Content Type

Formal Name

contentType [RFC2045, RFC2046]

Data Type

xs:string

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

5.1 About

If a service implements live preview, than the service MUST implement it as described in this section (§5). Live preview is be used to provide feedback to the client to, when applicable, signal capture and/or what is occurring during a capture.

5.2 Endpoints

Exposing endpoint information to a client is done through the service information. If live preview is implemented, the service information MUST contain key/value where the key is “livePreview” and the value is of type Parameter (§3.5). This must be a read-only parameter. The default value MUST be of type ResourceArray (§3.10). An implementation may expose one or more Resources (§3.11) in the ResourceArray. For the stream parameter, each instance of a Resource MUST 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 as it appears 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. The relationship field must only contain base-64 characters.


Example 24: The follow snippet is a skeleton service information entry for a stream parameter. Enclosing tags have been omitted.

<item>

  <key>livePreview</key>

  <value xsi:type=”Parameter”>

    <name>livePreview </name>

    <type>Resource</type>

    <readOnly>true</readOnly>

    <defaultValue xsi:type=”ResourceArray”>

      ...

      ...

    </defaultValue>

  </value>

</item>

Example 25: The following snippet is an example service information entry that exposes a Parameter (§3.5) 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>

  <value xsi:type=”Parameter”>

    <name>livePreview</name>

    <type>Resource</type>

    <readOnly>true</readOnly>

 

    <defaultValue xsi:type=”ResourceArray”>

      <element>

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

        <contentType>video/h264</contentType>

        <relationship>livePreview</relationship>

      </element>

      <element>

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

        <contentType>video/mpeg</contentType>

        <relationship>livePreview</relationship>

      </element>

    </defaultValue>

  </value>

</item>

Example 26: The following snippet is an example service information entry that exposes a Parameter (§3.5) 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>

  <value xsi:type=”Parameter”>

    <name>livePreview</name>

    <type>Resource</type>

    <readOnly>true</readOnly>

 

    <defaultValue xsi:type=”ResourceArray”>

      <element>

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

        <contentType>video/h264</contentType>

        <relationship>livePreview</relationship>

      </element>

      <element>

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

        <contentType>video/mpeg</contentType>

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

      </element>

    </defaultValue>

  </value>

</item>


To begin receiving live preview data, the client SHALL establish a connection to the desired live preview endpoint/URI. Closing the connection to an endpoint/URI SHALL terminate the transmission of all live preview data to establishing client. A client SHALL signal a capture using the capture operation (§6.13).

5.3 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.

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

Example 27: The following 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

 

0


6      Operations

6.1 About

This section, §6, provides detailed information regarding each WS-BD operation.

6.2 General Usage

6.2.1 Overview

The following usage requirements apply to all operations, unless the detailed documentation for a particular operation conflicts with these general requirements, 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 [RFC-HTTP].

6.     Namespace. A data type without an explicit namespace or namespace prefix implies it is a member of the wsbd namespace as defined in §3.2.

6.2.2 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 must 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 28: 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 §2.5.6 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 can only perform one capture at time) 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 why a client cannot receive a "sensorBusy" status if it does not hold the lock.


6.2.3 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 (§4.2), 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.

6.2.4 Visual Summaries (Informative)

6.2.4.1 Overview

The two tables in this subsection provide informative visual summaries of WS-BD operations. These visual summaries are an overview; they are not authoritative. (§6.4–6.17 are authoritative.)

6.2.4.2 Input & Output (Informative)

Table 7 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 §1.2).

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

Table 7. Summary of Operations Input/Output (informative)

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

/register

POST

none

l

 

l

 

6.4

unregister

/register/{sessionId}

DELETE

none

u

l

l

 

6.5

try lock

/lock/{sessionId}

POST

none

u

l

l

 

6.6

steal lock

PUT

none

u

l

l

 

6.7

unlock

DELETE

none

u

l

l

 

6.8

get service info

/info

GET

none

u

l

 

l

 

6.9

initialize

/initialize/{sessionId}

POST

none

u

n

l

l

 

6.10

get configuration

/configure/{sessionId}

GET

none

u

n

l

l

l

 

6.11

set configuration

POST

config

u

n

l

l

 

6.12

capture

/capture/{sessionId}

POST

none

n

l

l

l

 

6.13

download

/download/{captureid}

GET

none

u

l

l

l

l

6.14

get download info

/download/{captureid}/info

GET

none

u

 

 

 

 

l

 

 

6.15

thrifty download

/download/{captureid}/{maxSize}

GET

none

u

l

l

l

l

6.16

cancel operation

/cancel/{sessionId}

POST

none

u

n

l

l

 

6.17

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 29: 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 §6.13.


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.


6.2.4.3 Permitted Status Values (Informative)

Table 8 provides a visual summary of the status values permitted.

Table 8. Possible Status Values Per Operation (informative)

Status

Values

 

 

 

 

Operation
Description

success

failure

invalidId

canceled

canceledWithSensorFailure

sensorFailure

lockNotHeld

lockHeldByAnother

initializationNeeded

configurationNeeded

sensorBusy

sensorTimeout

unsupported

badValue

noSuchParameter

preparingDownload

register

l

l

unregister

l

l

l

l

l

try lock

l

l

l

l

l

steal lock

l

l

l

l

unlock

l

l

l

l

l

get service info

l

l

initialize

l

l

l

l

l

l

l

l

l

l

l

get configuration

l

l

l

l

l

l

l

l

l

l

l

l

l

set configuration

l

l

l

l

l

l

l

l

l

l

l

l

l

l

capture

l

l

l

l

l

l

l

l

l

l

l

l

l

download

l

l

l

l

l

get download info

l

l

l

 

 

 

 

 

 

 

 

 

 

l

 

l

thrifty download

l

l

l

l

l

l

cancel

l

l

l

l

l

l

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


Example 30: 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.

6.3 Documentation Conventions

6.3.1 About

Each WS-BD operation is documented according to the conventions described in this subsection (§6.3).

6.3.2 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 31: 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 (§2.5.8).

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 (§2.5.6) this value doubles as documentation as to whether or not a lock is required.

6.3.3 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 §3.2.

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

6.3.4 Usage

Each of the parts in this subsection describe the behaviors & requirements that are specific to its respective operation.

6.3.5 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 §2.2.

6.3.6 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 (§3.2) is inferred.

For example,
   badFields = { "sessionId" } (StringArray, §3.8)

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 §3.2.


6.4 Register

6.4.1 Overview

Description

Open a new client-server session

URL Template

/register

HTTP Method   

POST

URL Parameters

None

Input Payload

None

Idempotent

No

Sensor Operation

No

6.4.2 Result Summary

success

status = "success"

sessionId = session id (UUID, §3.3)

failure

status = "failure"

message* = informative message describing failure

6.4.3 Usage

Register provides a unique identifier that can be used to associate a particular client with a server.

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 4 (Informative): 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 (§2.5.4).

6.4.4 Unique Knowledge

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

6.4.5 Return Values Detail

6.4.5.1 Overview

The register operation must return a Result according to the constraints described in this subsection (§6.4.5).

6.4.5.2 Success

Status Value

success

Condition

The service accepts the registration request

Required Elements

status (Status, §3.13)

the literal "success"

sessionId (UUID, §3.3)

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.

6.4.5.3 Failure

Status Value

failure

Condition

The service cannot accept the registration request

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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.2 for how a client can use sensor metadata to determine the maximum number of current sessions a service can support.


6.5 Unregister

6.5.1 Overview

Description

Close a client-server session

URL Template

/register/{sessionId}

HTTP Method   

DELETE

URL Parameters

{sessionId} (UUID, §3.3)

Identity of the session to remove

Input Payload

None

Idempotent

Yes

Sensor Operation

No

6.5.2 Result Summary

success

status = "success"

failure

status = "failure"

message* = informative message describing failure

sensorBusy

status = "sensorBusy"

badValue

status = "badValue"
badFields = { "sessionId" } (StringArray, §3.8)

6.5.3 Usage

6.5.3.1 General

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.2 for details on connection metadata.)

6.5.3.2 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.2 for details on connection metadata.)

6.5.3.3 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 §2.5 for more information about client identity and the assumed security models.

6.5.3.4 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 §6.5.5.4).

6.5.4 Unique Knowledge

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

6.5.5 Return Values Detail

6.5.5.1 Overview

The unregister operation must return a Result according to the constraints described in this subsection (§6.5.5).

6.5.5.2 Success

Status Value

success

Condition

The service accepted the unregistration request

Required Elements

status (Status, §3.13)

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.

6.5.5.3 Failure

Status Value

failure

Condition

The service could not unregister the session.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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)

6.5.5.4 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, §3.13)

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 32: 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.


6.5.5.5 Bad Value

Status Value

badValue

Condition

The provided session id is not a well-formed UUID.

Required Elements

status (Status, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

an array that contains the single field name, "sessionId"

Optional Elements

None

See §6.2.3 for general information on how services must handle parameter failures.


6.6 Try Lock

6.6.1 Overview

Description

Try to obtain the service lock

URL Template

/lock/{sessionId}

HTTP Method   

POST

URL Parameters

{sessionId} (UUID, §3.3)

Identity of the session requesting the service lock

Input Payload

None

Idempotent

Yes

Sensor Operation

No

6.6.2 Result Summary

success

status = "success"

failure

status = "failure"

message* = informative message describing failure

invalidId

status = "invalidId"
badFields = { "sessionId" } (StringArray, §3.8)

lockHeldByAnother

status = "lockHeldByAnother"

badValue

status = "badValue"
badFields = { "sessionId" } (StringArray, §3.8)

6.6.3 Usage

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

6.6.4 Unique Knowledge

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

6.6.5 Return Values Detail

6.6.5.1 Overview

The try lock operation must return a Result according to the constraints described in this subsection (§6.6.5)

6.6.5.2 Success

Status Value

success

Condition

The service was successfully locked to the provided session id.

Required Elements

status (Status, §3.13)

the literal "success"

Optional Elements

None

Clients that hold the service lock are permitted to perform sensor operations (§2.5.6). By idempotency (§2.5.8), if a client already holds the lock, subsequent try lock operations MUST also return success.

6.6.5.3 Failure

Status Value

failure

Condition

The service could not be locked to the provided session id.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 §6.6.5.5 for an example).

6.6.5.4 Invalid Id

Status Value

invalidId

Condition

The provided session id is not registered with the service.

Required Elements

status (Status, §3.13)

the literal "invalidId"

badFields (StringArray, §3.8)

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 (§6.5.5.2).

See §6.2.3 for general information on how services must handle parameter failures.

6.6.5.5 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, §3.13)

the literal "lockHeldByAnother"

Optional Elements

None


Example 33: 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.


6.6.5.6 Bad Value

Status Value

badValue

Condition

The provided session id is not a well-formed UUID.

Required Elements

status (Status, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

an array that contains the single field name, "sessionId"

Optional Elements

None

See §6.2.3 for general information on how services must handle parameter failures.


6.7 Steal Lock

6.7.1 Overview

Description

Forcibly obtain the lock away from a peer client

URL Template

/lock/{sessionId}

HTTP Method   

PUT

URL Parameters

{sessionId} (UUID, §3.3)

Identity of the session requesting the service lock

Input Payload

None

Idempotent

Yes

Sensor Operation

No

6.7.2 Result Summary

success

status = "success"

failure

status = "failure"

message* = informative message describing failure

invalidId

status = "invalidId"
badFields = { "sessionId" } (StringArray, §3.8)

badValue

status = "badValue"
badFields = { "sessionId" } (StringArray, §3.8)

6.7.3 Usage

6.7.3.1 General

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.

6.7.3.2 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.

6.7.3.3 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.

6.7.3.4 Cancellation & (Lack of) Client Notification

Lock stealing must not affect any currently running sensor operations. That is, it must be possible that a client initiates a sensor operation, has its lock stolen away, and have the operation completes successfully anyway. 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.

6.7.4 Unique Knowledge

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

6.7.5 Return Values Detail

6.7.5.1 Overview

The steal lock operation must return a Result according to the constraints described in this subsection (§6.7.5).

6.7.5.2 Success

Status Value

Success

Condition

The service was successfully locked to the provided session id.

Required Elements

status (Status, §3.13)

the literal "success"

Optional Elements

None

See §2.5.6 for detailed information about the WS-BD concurrency and locking model. Cancellation must have no effect on pending sensor operations (§6.7.3.4).

6.7.5.3 Failure

Status Value

failure

Condition

The service could not be locked to the provided session id.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 (§6.7.3.3). 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.

6.7.5.4 Invalid Id

Status Value

invalidId

Condition

The provided session id is not registered with the service.

Required Elements

status (Status, §3.13)

the literal "invalidId"

badFields (StringArray, §3.8)

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 (§6.5.5.2).

See §6.2.3 for general information on how services must handle parameter failures.

6.7.5.5 Bad Value

Status Value

badValue

Condition

The provided session id is not a well-formed UUID.

Required Elements

status (Status, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

an array that contains the single field name, "sessionId"

Optional Elements

None

See §6.2.3 for general information on how services must handle parameter failures.


6.8 Unlock

6.8.1 Overview

Description

Release the service lock

URL Template

/lock/{sessionId}

HTTP Method   

DELETE

URL Parameters

{sessionId} (UUID, §3.3)

Identity of the session releasing the service lock

Input Payload

None

Idempotent

Yes

Sensor Operation

No

6.8.2 Result Summary

success

status = "success"

failure

status = "failure"

message* = informative message describing failure

invalidId

status = "invalidId"
badFields = { "sessionId" } (StringArray, §3.8)

badValue

status = "badValue"
badFields = { "sessionId" } (StringArray, §3.8)

6.8.3 Usage

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

See §2.5.6 for detailed information about the WS-BD concurrency and locking model.

6.8.4 Unique Knowledge

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

6.8.5 Return Values Detail

6.8.5.1 Overview

The steal lock operation must return a Result according to the constraints described in this subsection (§6.8.5).

6.8.5.2 Success

Status Value

success

Condition

The service returned to an unlocked state.

Required Elements

status (Status, §3.13)

the literal "success"

Optional Elements

None

Upon releasing the lock, a client is no longer permitted to perform any sensor operations (§2.5.6). By idempotency (§2.5.8), if a client already has released the lock, subsequent unlock operations should also return success.

6.8.5.3 Failure

Status Value

failure

Condition

The service could not be transitioned into an unlocked state.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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.

6.8.5.4 Invalid Id

Status Value

invalidId

Condition

The provided session id is not registered with the service.

Required Elements

status (Status, §3.13)

the literal "invalidId"

badFields (StringArray, §3.8)

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 (§6.5.5.2).

See §6.2.3 for general information on how services must handle parameter failures.

6.8.5.5 Bad Value

Status Value

badValue

Condition

The provided session id is not a well-formed UUID.

Required Elements

status (Status, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

an array that contains the single field name, "sessionId"

Optional Elements

None

See §6.2.3 for general information on how services must handle parameter failures.


6.9 Get Service Info

6.9.1 Overview

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

6.9.2 Result Summary

success

status = "success"

metadata = dictionary containing service metadata (Dictionary, §3.4)

failure

status = "failure"

message* = informative message describing failure

6.9.3 Usage

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 §4.2 for information about the metadata returned from this operation.


Example 34: 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 35: The following is the ‘raw’ response from the above request. The metadata element of the result contains a Dictionary (§3.4) of parameter names and parameter information represented as a Parameter (§3.5).

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

 

<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>

  <metadata>

    <item>

      <key>width</key>

      <value i:type="Parameter">

        <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>

        <defaultValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">800</defaultValue>

        <allowedValues>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">1280</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">960</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">800</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">640</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">424</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">416</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">352</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">320</allowedValue>

        </allowedValues>

      </value>

    </item>

    <item>

      <key>height</key>

      <value i:type="Parameter">

        <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>

        <defaultValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">600</defaultValue>

        <allowedValues>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">720</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">600</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">544</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">480</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">448</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">360</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">288</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">240</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">144</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">120</allowedValue>

        </allowedValues>

      </value>

    </item>

    <item>

      <key>frameRate</key>

      <value i:type="Parameter">

        <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>

        <defaultValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">30</defaultValue>

        <allowedValues>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">30</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">15</allowedValue>

          <allowedValue i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">10</allowedValue>

        </allowedValues>

      </value>

    </item>

    <item>

      <key>modality</key>

      <value i:type="Parameter">

        <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>

        <readOnly>true</readOnly>

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

      </value>

    </item>

    <item>

      <key>submodality</key>

      <value i:type="Parameter">

        <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>

        <readOnly>true</readOnly>

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

      </value>

    </item>

  </metadata>

</result>


6.9.4 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).

6.9.5 Return Values Detail

6.9.5.1 Overview

The get service info operation must return a Result according to constraints described in this subsection (§6.9.5).

6.9.5.2 Success

Status Value

success

Condition

The service provides service metadata

Required Elements

status (Status, §3.13)

the literal "success"

metadata (Dictionary, §3.4)

information about the service metadata

Optional Elements

None

6.9.5.3 Failure

Status Value

failure

Condition

The service cannot provide service metadata

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

an informative description of the nature of the failure

 


6.10 Initialize

6.10.1 Overview

Description

Initialize the target biometric sensor

URL Template

/initialize/{sessionId}

HTTP Method   

POST         

URL Parameters

{sessionId} (UUID, §3.3)

Identity of the session requesting initialization

Input Payload

None

Idempotent

Yes

Sensor Operation

Yes

6.10.2 Result Summary

success

status = "success"

failure

status = "failure"

message* = informative message describing failure

invalidId

status = "invalidId"
badFields = { "sessionId" } (StringArray, §3.8)

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, §3.8)

6.10.3 Usage

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.

6.10.4 Unique Knowledge

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

6.10.5 Return Values Detail

6.10.5.1 Overview

The initialize operation must return a Result according to constraints described in this subsection (§6.10.5).

6.10.5.2 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

6.10.5.3 Failure

Status Value

failure

Condition

The service experienced a fault that prevented successful initialization.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 (§6.10.5.6, §6.10.5.7)

6.10.5.4 Invalid Id

Status Value

invalidId

Condition

The provided session id is not registered with the service.

Required Elements

status (Status, §3.13)

the literal "invalidId"

badFields (StringArray, §3.8)

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 (§6.5.5.2).

See §6.2.3 for general information on how services must handle parameter failures.

6.10.5.5 Canceled

Status Value

canceled

Condition

The initialization operation was interrupted by a cancellation request.

Required Elements

status (Status, §3.13)

the literal "canceled"

Optional Elements

None

See §6.17.3.3 for information about what may trigger a cancellation.

6.10.5.6 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, §3.13)

the literal "canceledWithSensorFailure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 §6.17.3.3 for information about what may trigger a cancellation.

6.10.5.7 Sensor Failure

Status Value

sensorFailure

Condition

The initialization failed due to a failure within the target biometric sensor

Required Elements

status (Status, §3.13)

the literal "sensorFailure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 (§6.10.5.3).

6.10.5.8 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, §3.13)

the literal "lockNotHeld"

Optional Elements

None

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

6.10.5.9 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, §3.13)

the literal "lockHeldByAnother"

Optional Elements

None

6.10.5.10 Sensor Busy

Status Value

sensorBusy

Condition

If the initialization could not be performed because the service is already performing a sensor operation.

Required Elements

status (Status, §3.13)

the literal "sensorBusy"

Optional Elements

None

6.10.5.11 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, §3.13)

the literal "sensorTimeout"

Optional Elements

None

A service did not receive a timely response from the target biometric sensor. This condition is distinct from the client’s originating HTTP request, which may have its own, independent timeout.  (See A.3 for information on how a client might determine timeouts.)

6.10.5.12 Bad Value

Status Value

badValue

Condition

The provided session id is not a well-formed UUID.

Required Elements

status (Status, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

an array that contains the single field name, "sessionId"

Optional Elements

None

See §6.2.3 for general information on how services must handle parameter failures.


6.11 Get Configuration

6.11.1 Overview

Description

Retrieve metadata about the target biometric sensor’s current configuration

URL Template

/configure/{sessionId}

HTTP Method   

GET          

URL Parameters

{sessionId} (UUID, §3.3)

Identity of the session requesting the configuration

Input Payload

None

Idempotent

Yes

Sensor Operation

Yes

6.11.2 Result Summary

success

status = "success"
metadata = current configuration of the sensor (Dictionary, §3.4)

failure

status = "failure"

message* = informative message describing failure

invalidId

status = "invalidId"
badFields = { "sessionId" } (StringArray, §3.8)

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, §3.8)

6.11.3 Usage

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


Example 36: 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 37: The following is the ‘raw’ response from the previous request. The metadata element in the result contains a Dictionary (§3.4) 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>

  <metadata>

    <item>

      <key>width</key>

      <value i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">800</value>

    </item>

    <item>

      <key>height</key>

      <value i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">600</value>

    </item>

    <item>

      <key>frameRate</key>

      <value i:type="a:int" xmlns:a="http://www.w3.org/2001/XMLSchema">15</value>

    </item>

  </metadata>

</result>


6.11.4 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.

6.11.5 Return Values Detail

6.11.5.1 Overview

The get configuration operation must return a Result according to the constraints described in this subsection (§6.11.5).

6.11.5.2 Success

Status Value

success

Condition

The service provides the current configuration

Required Elements

status (Status, §3.13)

the literal "success"

metadata (Dictionary, §3.4)

the target biometric sensor’s current configuration

Optional Elements

None

See §4.3 for information regarding configurations.

6.11.5.3 Failure

Status Value

failure

Condition

The service cannot provide the current configuration due to service (not target biometric sensor) error.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 §6.11.5.6, §6.11.5.7).

6.11.5.4 Invalid Id

Status Value

invalidId

Condition

The provided session id is not registered with the service.

Required Elements

status (Status, §3.13)

the literal "invalidId"

badFields (StringArray, §3.8)

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 (§6.5.5.2).

See §6.2.3 for general information on how services must handle parameter failures.

6.11.5.5 Canceled

Status Value

canceled

Condition

The get configuration operation was interrupted by a cancellation request.

Required Elements

status (Status, §3.13)

the literal "canceled"

Optional Elements

None

See §6.17.3.3 for information about what may trigger a cancellation.

6.11.5.6 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, §3.13)

the literal "canceledWithSensorFailure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 §6.17.3.3 for information about what may trigger a cancellation.

6.11.5.7 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, §3.13)

the literal "sensorFailure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 (§6.10.5.3).

6.11.5.8 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, §3.13)

the literal "lockNotHeld"

Optional Elements

None

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

6.11.5.9 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, §3.13)

the literal "lockHeldByAnother"

Optional Elements

None

6.11.5.10 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, §3.13)

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.

6.11.5.11 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, §3.13)

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.

6.11.5.12 Sensor Busy

Status Value

sensorBusy

Condition

If the configuration could not be queried because the service is already performing a sensor operation.

Required Elements

status (Status, §3.13)

the literal "sensorBusy"

Optional Elements

None

6.11.5.13 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, §3.13)

the literal "sensorTimeout"

Optional Elements

None

A sensorTimeout result indicates that the service did not receive a timely response from the target biometric sensor. This condition is distinct from the client’s originating HTTP request, which may have its own, independent timeout.  (See A.3 for information on how a client might determine timeouts.)

6.11.5.14 Bad Value

Status Value

badValue

Condition

The provided session id is not a well-formed UUID.

Required Elements

status (Status, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

an array that contains the single field name, "sessionId"

Optional Elements

None

See §6.2.3 for general information on how services must handle parameter failures.


6.12 Set Configuration

6.12.1 Overview

Description

Set the target biometric sensor’s configuration

URL Template

/configure/{sessionId}

HTTP Method   

POST         

URL Parameters

{sessionId} (UUID, §3.3)

Identity of the session setting the configuration

Input Payload

Desired sensor configuration (Dictionary, §3.4)

Idempotent

Yes

Sensor Operation

Yes

6.12.2 Result Summary

success

status = "success"

failure

status = "failure"

message* = informative message describing failure

invalidId

status = "invalidId"
badFields = { "sessionId" } (StringArray, §3.8)

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, §3.8)

badValue

status = "badValue"
badFields = {"sessionId"} (StringArray, §3.8)

   (or)

status = "badValue"

badFields = { field names } (StringArray, §3.8)

noSuchParameter

status = "unsupported"

badFields = { field names } (StringArray, §3.8)

6.12.3 Usage

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

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 (§3.4) element named configuration. See §4.3 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 38: 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

 

<configuration xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://docs.oasis-open.org/biometrics/ns/ws-bd-1.0">

  <item>

    <key>width</key>

    <value xmlns:d3p1="http://www.w3.org/2001/XMLSchema" i:type="d3p1:int">800</value>

  </item>

  <item>

    <key>height</key>

    <value xmlns:d3p1="http://www.w3.org/2001/XMLSchema" i:type="d3p1:int">600</value>

  </item>

  <item>

    <key>frameRate</key>

    <value xmlns:d3p1="http://www.w3.org/2001/XMLSchema" i:type="d3p1:int">15</value>

  </item>

</configuration>


More information regarding the use of the xmlns attribute can be found in [XML-NAMES].

6.12.4 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).

6.12.5 Return Values Detail

6.12.5.1 Overview

The set configuration operation must return a Result according to the constraints described in this subsection (§6.12.5).

6.12.5.2 Success

Status Value

success

Condition

The service was able to successfully set the full configuration

Required Elements

status (Status, §3.13)

the literal "success"

Optional Elements

None

6.12.5.3 Failure

Status Value

failure

Condition

The service cannot set the desired configuration due to service (not target biometric sensor) error.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 §6.12.5.6, §6.12.5.7).

6.12.5.4 Invalid Id

Status Value

invalidId

Condition

The provided session id is not registered with the service.

Required Elements

status (Status, §3.13)

the literal "invalidId"

badFields (StringArray, §3.8)

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 (§6.5.5.2).

6.12.5.5 Canceled

Status Value

canceled

Condition

The set configuration operation was interrupted by a cancellation request.

Required Elements

status (Status, §3.13)

the literal "canceled"

Optional Elements

None

See §6.17.3.3 for information about what may trigger a cancellation.

6.12.5.6 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, §3.13)

the literal "canceledWithSensorFailure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 §6.17.3.3 for information about what may trigger a cancellation.

6.12.5.7 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, §3.13)

the literal "sensorFailure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 (§6.12.5.3). Errors with the configuration itself should be reported via an unsupported (§6.12.5.13), badValue (§6.12.5.14), or badValue  status (§6.12.5.15).

6.12.5.8 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, §3.13)

the literal "lockNotHeld"

Optional Elements

None

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

6.12.5.9 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, §3.13)

the literal "lockHeldByAnother"

Optional Elements

None

6.12.5.10 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, §3.13)

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.

6.12.5.11 Sensor Busy

Status Value

sensorBusy

Condition

If the configuration could not be performed because the service is already performing a sensor operation.

Required Elements

status (Status, §3.13)

the literal "sensorBusy"

Optional Elements

None

6.12.5.12 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, §3.13)

the literal "sensorTimeout"

Optional Elements

None

A sensorTimeout result indicates that the 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.3 for information on how a client might determine timeouts.)

6.12.5.13 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, §3.13)

the literal "unsupported"

badFields (StringArray, §3.8)

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 (i.e., there is no direct mechanism for encoding co-occurrence constraints).  See §6.2.3 for additional information on how services must handle parameter failures.


Example 39: A WS-BD service uses 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


6.12.5.14 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, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

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

6.12.5.15 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, §3.13)

the literal "noSuchParameter"

badFields (StringArray, §3.8)

an array that contains the field name(s) that are not recognized by the service

Optional Elements

None

See §6.2.3 for general information on how services must handle parameter failures.


6.13 Capture

6.13.1 Overview

Description

Capture biometric data

URL Template

/capture/{sessionId}

HTTP Method   

POST         

URL Parameters

{sessionId} (UUID, §3.3)

Identity of the session requesting the capture

Input Payload

None

Idempotent

No

Sensor Operation

Yes

6.13.2 Result Summary

success

status = "success"

captureIds = { identifiers of captured data } (UuidArray, §3.9)

failure

status = "failure"

message* = informative message describing failure

invalidId

status = "invalidId"
badFields = { "sessionId" } (StringArray, §3.8)

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, §3.8)

6.13.3 Usage

6.13.3.1 General

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: 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 (§6.14.3.3)

6.13.3.2 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.3.5), and clients can automatically adjust their own timeouts and behavior accordingly.

6.13.4 Unique Knowledge

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

6.13.5 Return Values Detail

6.13.5.1 Overview

The capture operation must return a Result according to the constraints described in this subsection (§6.13.5).

6.13.5.2 Success

Status Value

success

Condition

The service successfully performed a biometric acquisition

Required Elements

status (Status, §3.13)

the literal "success"

captureIds (UuidArray, §3.9)

one more UUIDs that uniquely identify the data acquired by the operation

Optional Elements

None

See the usage requirements for capture (§6.13.3) and download (§6.14.3) for full detail.

6.13.5.3 Failure

Status Value

failure

Condition

The service cannot perform the capture due to a service (not target biometric sensor) error.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 §6.13.5.6, §6.13.5.7).  A service may fail at capture if there is not enough internal storage available to accommodate the captured data (§A.4).

6.13.5.4 Invalid Id

Status Value

invalidId

Condition

The provided session id is not registered with the service.

Required Elements

status (Status, §3.13)

the literal "invalidId"

badFields (StringArray, §3.8)

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 (§6.5.5.2).

See §6.2.3 for general information on how services must handle parameter failures.

6.13.5.5 Canceled

Status Value

canceled

Condition

The capture operation was interrupted by a cancellation request.

Required Elements

status (Status, §3.13)

the literal "canceled"

Optional Elements

None

See §6.17.3.3 for information about what may trigger a cancellation.

6.13.5.6 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, §3.13)

the literal "canceledWithSensorFailure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 §6.17.3.3 for information about what may trigger a cancellation.

6.13.5.7 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, §3.13)

the literal "sensorFailure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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 (§6.13.5.3).

6.13.5.8 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, §3.13)

the literal "lockNotHeld"

Optional Elements

None

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

6.13.5.9 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, §3.13)

the literal "lockHeldByAnother"

Optional Elements

None

6.13.5.10 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, §3.13)

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.

6.13.5.11 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, §3.13)

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.

6.13.5.12 Sensor Busy

Status Value

sensorBusy

Condition

If the capture could not be performed because the service is already performing a sensor operation.

Required Elements

status (Status, §3.13)

the literal "sensorBusy"

Optional Elements

None

6.13.5.13 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, §3.13)

the literal "sensorTimeout"

Optional Elements

None

A sensorTimeout result indicates that the 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.3 for information on how a client might determine timeouts.)

6.13.5.14 Bad Value

Status Value

badValue

Condition

The provided session id is not a well-formed UUID.

Required Elements

status (Status, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

an array that contains the single field name, "sessionId"

Optional Elements

None

See §6.2.3 for general information on how services must handle parameter failures.


6.14 Download

6.14.1 Overview

Description

Download the captured biometric data

URL Template

/download/{captureId}

HTTP Method   

GET

URL Parameters

{captureId} (UUID, §3.3)

Identity of the captured data to download

Input Payload

None

Idempotent

Yes

Sensor Operation

No

6.14.2 Result Summary

success

status = "success"

metadata = sensor configuration at the time of capture (Dictionary, §3.4)
sensorData = biometric data (xs:base64Binary)

failure

status = "failure"

message* = informative message describing failure

invalidId

status = "invalidId"
badFields = { "captureId" } (StringArray, §3.8)

badValue

status = "badValue"
badFields = { "captureId" } (StringArray, §3.8)

preparingDownload

status = "preparingDownload"

6.14.3 Usage

6.14.3.1 General

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

6.14.3.2 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.

6.14.3.3 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 40: A service exposing a fingerprint scanner also performs post processing on a fingerprint image—segmentation, quality assessment, and templatization.

 

Example 41: 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 42: 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 43: 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 involves 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 44: 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. 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.

6.14.3.4 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.3.6)

6.14.4 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.

6.14.5 Return Values Detail

6.14.5.1 Overview

The download operation must return a Result according to the constraints described in this section (§6.14.5).

6.14.5.2 Success

Status Value

success

Condition

The service can provide the requested data

Required Elements

status (Status, §3.13)

the literal "success"

metadata (Dictionary, §3.4)

sensor metadata as it was at the time of capture

sensorData (xs:base64Binary, [XMSCHEMA-2])

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 requirements for both capture (§6.13.3) and download (§6.14.3) for more detail regarding the conditions under which a service is permitted to accept or deny download requests.

6.14.5.3 Failure

Status Value

failure

Condition

The service cannot provide the requested data.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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.

6.14.5.4 Invalid Id

Status Value

invalidId

Condition

The provided capture id is not recognized by the service.

Required Elements

status (Status, §3.13)

the literal "invalidId"

badFields (StringArray, §3.8)

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.4).

See §6.2.3 for general information on how services must handle parameter failures.

6.14.5.5 Bad Value

Status Value

badValue

Condition

The provided capture id is not a well-formed UUID.

Required Elements

status (Status, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

an array that contains the single field name, "captureId"

Optional Elements

None

See §6.2.3 for general information on how services must handle parameter failures.

6.14.5.6 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, §3.13)

the literal "preparingDownload"

Optional Elements

None

See the Us for both capture (§6.13.3) and download (§6.14.3) for full detail.

 


6.15 Get Download Info

6.15.1 Overview

Description

Get only the metadata associated with a particular capture

URL Template

/download/{captureId}/info

HTTP Method   

GET

URL Parameters

{captureId} (UUID, §3.3)

Identity of the captured data to query

Input Payload

Not applicable

Idempotent

Yes

Sensor Operation

No

6.15.2 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, §3.8)

badValue

status = "badValue"
badFields = { "captureId" } (StringArray, §3.8)

preparingDownload

status = "preparingDownload"

6.15.3 Usage

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 requirements for download (§6.15.3) also apply to get download info.

6.15.4 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.

6.15.5 Return Values Detail

6.15.5.1 Overview

The get download info operation must return a Result according to the constraints described in this subsection (§6.15.5).

6.15.5.2 Success

Status Value

success

Condition

The service can provide the requested data

Required Elements

status (Status, §3.13)

the literal "success"

metadata (Dictionary, §3.4)

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 (§6.14.5.2), but without the sensor data.

6.15.5.3 Failure

Status Value

failure

Condition

The service cannot provide the requested data.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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.

6.15.5.4 Invalid Id

Status Value

invalidId

Condition

The provided capture id is not recognized by the service.

Required Elements

status (Status, §3.13)

the literal "invalidId"

badFields (StringArray, §3.8)

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.4).

See §6.2.3 for general information on how services must handle parameter failures.

6.15.5.5 Bad Value

Status Value

badValue

Condition

The provided capture id is not a well-formed UUID.

Required Elements

status (Status, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

an array that contains the single field name, "captureId"

Optional Elements

None

See §6.2.3 for general information on how services must handle parameter failures.

6.15.5.6 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, §3.13)

the literal "preparingDownload"

Optional Elements

None

See the usage requirements for both capture (§6.13.3) and download (§6.14.3) for full detail.


6.16 Thrifty Download

6.16.1 Overview

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, §3.3)

Identity of the captured data to download

{maxSize} (xs:string, [XMSCHEMA-2])

Content-type dependent indicator of maximum permitted download size

Input Payload

None

Idempotent

Yes

Sensor Operation

No

6.16.2 Result Summary

success

status = "success"
metadata = minimal metadata describing the captured data (Dictionary, §3.4, §4.4.2)

sensorData = biometric data (xs:base64Binary)

failure

status = "failure"

message* = informative message describing failure

invalidId

status = "invalidId"

badFields = {"captureId"} (StringArray, §3.8)

badValue

status = "badValue"
badFields =
either "captureId", "maxSize", or both (StringArray, §3.8)

unsupported

status = "unsupported"

preparingDownload

status = "preparingDownload"

6.16.3 Usage

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 requirements for download (§6.15.3) 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.)

6.16.4 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).

6.16.5 Return Values Detail

6.16.5.1 Overview

The thrifty download operation must return a Result according to the constraints described in this subsection (§6.16.5).

6.16.5.2 Success

Status Value

success

Condition

The service can provide the requested data

Required Elements

status (Status, §3.13)

the literal "success"

metadata (Dictionary, §3.4)

minimal representation of sensor metadata as it was at the time of capture. See §4.4.2 for information regarding minimal metadata.

sensorData (xs:base64Binary, [XMSCHEMA-2])

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.

6.16.5.3 Failure

Status Value

failure

Condition

The service cannot provide the requested data.

Required Elements

status (Status, §3.13)

the literal "failure"

Optional Elements

message (xs:string, [XMSCHEMA-2])

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.

6.16.5.4 Invalid Id

Status Value

invalidId

Condition

The provided capture id is not recognized by the service.

Required Elements

status (Status, §3.13)

the literal "invalidId"

badFields (StringArray, §3.8)

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.4).

See §6.2.3 for general information on how services must handle parameter failures.

6.16.5.5 Bad Value

Status Value

badValue

Condition

The provided capture id is not a well-formed UUID.

Required Elements

status (Status, §3.13)

the literal "badValue"

badFields (StringArray, §3.8)

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

6.16.5.6 Unsupported

Status Value

unsupported

Condition

The service does not support thrifty download

Required Elements

status (Status, §3.13)

the literal "unsupported"

Optional Elements

None

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

6.16.5.7 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, §3.13)

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 §6.14.3.3 for detail.


6.17 Cancel

6.17.1 Overview

Description

Cancel the current sensor operation

URL Template

/cancel/{sessionId}

HTTP Method   

POST

URL Parameters

{sessionId} (UUID, §3.3)

Identity of the session requesting cancellation

Input Payload

None

Idempotent

Yes

Sensor Operation

Yes

6.17.2 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"}

6.17.3 Usage

6.17.3.1 General

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