Extensible Resource Identifier (XRI) Resolution Version 2.0
Committee Specification 01
12 April 2008
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Technical Committee:
OASIS eXtensible Resource Identifier (XRI) TC
Chairs:
Gabe Wachob, AmSoft <gabe.wachob@amsoft.net>
Drummond Reed, Cordance <drummond.reed@cordance.net>
Editors:
Gabe Wachob, AmSoft <gabe.wachob@amsoft.net>
Drummond Reed, Cordance <drummond.reed@cordance.net>
Les Chasen, NeuStar <les.chasen@neustar.biz>
William Tan, NeuStar <william.tan@neustar.biz>
Steve Churchill, XDI.org <steven.churchill@xdi.org>
Related Work:
This specification replaces or supercedes:
This specification is related to:
Declared XML Namespace(s)
xri://$res
xri://$xrds
xri://$xrd
xri://$xrd*($v*2.0)
xri://$res*auth
xri://$res*auth*($v*2.0)
xri://$res*proxy
xri://$res*proxy*($v*2.0)
Abstract:
This document defines a simple generic format for resource description (XRDS documents), a protocol for obtaining XRDS documents from HTTP(S) URIs, and generic and trusted protocols for resolving Extensible Resource Identifiers (XRIs) using XRDS documents and HTTP(S) URIs. These protocols are intended for use with both HTTP(S) URIs as defined in [RFC2616] and with XRIs as defined by Extensible Resource Identifier (XRI) Syntax Version 2.0 [XRISyntax] or higher. For a dictionary of XRIs defined to provide standardized identifier metadata, see Extensible Resource Identifier (XRI) Metadata Version 2.0 [XRIMetadata]. For a basic introduction to XRIs, see the XRI 2.0 FAQ [XRIFAQ].
Status:
This document was last revised or approved by the XRI Technical Committee on the above date. The level of approval is also listed above. Check the “Latest Version” or “Latest Approved Version” location noted above for possible later revisions of this document.
Technical Committee members should send comments on this specification to the Technical Committee’s email list. Others should send comments to the Technical Committee by using the “Send A Comment” button on the Technical Committee’s web page at http://www.oasis-open.org/committees/xri.
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 (http://www.oasis-open.org/committees/xri/ipr.php.
The non-normative errata page for this specification is located at http://www.oasis-open.org/committees/xri.
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Table of Contents
1 Introduction.............................................................................................................................. 11
1.1 Overview of XRI Resolution Architecture................................................................................... 11
1.2 Structure of this Specification.................................................................................................. 14
1.3 Terminology and Notation........................................................................................................ 15
1.4 Examples............................................................................................................................... 15
1.5 Normative References............................................................................................................. 15
1.6 Non-Normative References...................................................................................................... 16
2 Conformance........................................................................................................................... 17
2.1 Conformance Targets.............................................................................................................. 17
2.2 Conformance Claims............................................................................................................... 17
2.3 XRDS Clients.......................................................................................................................... 17
2.4 XRDS Servers........................................................................................................................ 17
2.5 XRI Local Resolvers................................................................................................................ 18
2.5.1 Generic............................................................................................................................ 18
2.5.2 HTTPS............................................................................................................................. 18
2.5.3 SAML.............................................................................................................................. 18
2.6 XRI Proxy Resolvers............................................................................................................... 18
2.6.1 Generic............................................................................................................................ 18
2.6.2 HTTPS............................................................................................................................. 18
2.6.3 SAML.............................................................................................................................. 18
2.7 XRI Authority Servers.............................................................................................................. 19
2.7.1 Generic............................................................................................................................ 19
2.7.2 HTTPS............................................................................................................................. 19
2.7.3 SAML.............................................................................................................................. 19
2.8 Extensions............................................................................................................................. 19
2.9 Language............................................................................................................................... 19
3 Namespaces............................................................................................................................ 20
3.1 XRI Namespaces for XRI Resolution........................................................................................ 20
3.1.1 XRIs Reserved for XRI Resolution..................................................................................... 20
3.1.2 XRIs Assigned to XRI Resolution Service Types................................................................ 20
3.2 XML Namespaces for XRI Resolution....................................................................................... 21
3.3 Media Types for XRI Resolution............................................................................................... 21
4 XRDS Documents.................................................................................................................... 23
4.1 XRDS and XRD Namespaces and Schema Locations............................................................... 23
4.2 XRD Elements and Attributes.................................................................................................. 23
4.2.1 Management Elements..................................................................................................... 25
4.2.2 Trust Elements................................................................................................................. 26
4.2.3 Synonym Elements.......................................................................................................... 27
4.2.4 Service Endpoint Descriptor Elements.............................................................................. 27
4.2.5 Service Endpoint Trust Elements....................................................................................... 29
4.2.6 Service Endpoint Selection Elements................................................................................ 29
4.3 XRD Attribute Processing Rules.............................................................................................. 30
4.3.1 ID Attribute...................................................................................................................... 30
4.3.2 Version Attribute.............................................................................................................. 30
4.3.3 Priority Attribute............................................................................................................... 30
4.4 XRI and IRI Encoding Requirements......................................................................................... 31
5 XRD Synonym Elements........................................................................................................... 32
5.1 Query Identifiers...................................................................................................................... 32
5.1.1 HTTP(S) URI Query Identifiers........................................................................................... 32
5.1.2 XRI Query Identifiers......................................................................................................... 32
5.2 Synonym Elements................................................................................................................. 33
5.2.1 LocalID............................................................................................................................ 33
5.2.2 EquivID........................................................................................................................... 33
5.2.3 CanonicalID..................................................................................................................... 34
5.2.4 CanonicalEquivID............................................................................................................. 34
5.3 Redirect and Ref Elements...................................................................................................... 35
5.4 XRD Equivalence.................................................................................................................... 35
5.5 Synonym Verification.............................................................................................................. 36
5.6 Synonym Selection................................................................................................................. 36
6 Discovering an XRDS Document from an HTTP(S) URI............................................................... 37
6.1 Overview................................................................................................................................ 37
6.2 HEAD Protocol....................................................................................................................... 37
6.3 GET Protocol.......................................................................................................................... 37
7 XRI Resolution Flow................................................................................................................. 39
8 Inputs and Outputs................................................................................................................... 41
8.1 Inputs..................................................................................................................................... 41
8.1.1 QXRI (Authority String, Path String, and Query String)........................................................ 43
8.1.2 Resolution Output Format................................................................................................. 43
8.1.3 Service Type.................................................................................................................... 44
8.1.4 Service Media Type.......................................................................................................... 45
8.2 Outputs.................................................................................................................................. 45
8.2.1 XRDS Document.............................................................................................................. 47
8.2.2 XRD Element................................................................................................................... 47
8.2.3 URI List............................................................................................................................ 48
8.2.4 HTTP(S) Redirect.............................................................................................................. 48
9 Generic Authority Resolution Service......................................................................................... 49
9.1 XRI Authority Resolution.......................................................................................................... 49
9.1.1 Service Type and Service Media Type............................................................................... 49
9.1.2 Protocol.......................................................................................................................... 50
9.1.3 Requesting an XRDS Document using HTTP(S)................................................................. 52
9.1.4 Failover Handling............................................................................................................. 53
9.1.5 Community Root Authorities............................................................................................. 54
9.1.6 Self-Describing XRDS Documents.................................................................................... 55
9.1.7 Qualified Subsegments.................................................................................................... 55
9.1.8 Cross-References............................................................................................................. 56
9.1.9 Selection of the Next Authority Resolution Service Endpoint.............................................. 56
9.1.10 Construction of the Next Authority URI............................................................................. 57
9.1.11 Recursing Authority Resolution........................................................................................ 57
9.2 IRI Authority Resolution........................................................................................................... 58
9.2.1 Service Type and Media Type........................................................................................... 58
9.2.2 Protocol.......................................................................................................................... 58
9.2.3 Optional Use of HTTPS.................................................................................................... 58
10 Trusted Authority Resolution Service......................................................................................... 60
10.1 HTTPS.................................................................................................................................. 60
10.1.1 Service Type and Service Media Type............................................................................. 60
10.1.2 Protocol......................................................................................................................... 60
10.2 SAML................................................................................................................................... 60
10.2.1 Service Type and Service Media Type............................................................................. 61
10.2.2 Protocol......................................................................................................................... 61
10.2.3 Recursing Authority Resolution........................................................................................ 62
10.2.4 Client Validation of XRDs............................................................................................... 63
10.2.5 Correlation of ProviderID and KeyInfo Elements............................................................... 64
10.3 HTTPS+SAML....................................................................................................................... 64
10.3.1 Service Type and Service Media Type............................................................................. 64
10.3.2 Protocol......................................................................................................................... 65
11 Proxy Resolution Service.......................................................................................................... 66
11.1 Service Type and Media Types.............................................................................................. 66
11.2 HXRIs................................................................................................................................... 66
11.3 HXRI Query Parameters......................................................................................................... 67
11.4 HXRI Encoding/Decoding Rules............................................................................................. 68
11.5 HTTP(S) Accept Headers....................................................................................................... 70
11.6 Null Resolution Output Format............................................................................................... 70
11.7 Outputs and HTTP(S) Redirects.............................................................................................. 70
11.8 Differences Between Proxy Resolution Servers....................................................................... 71
11.9 Combining Authority and Proxy Resolution Servers................................................................. 71
12 Redirect and Ref Processing..................................................................................................... 72
12.1 Cardinality............................................................................................................................. 74
12.2 Precedence........................................................................................................................... 74
12.3 Redirect Processing.............................................................................................................. 75
12.4 Ref Processing..................................................................................................................... 76
12.5 Nested XRDS Documents..................................................................................................... 77
12.5.1 Redirect Examples......................................................................................................... 77
12.5.2 Ref Examples................................................................................................................ 81
12.6 Recursion and Backtracking................................................................................................... 84
13 Service Endpoint Selection....................................................................................................... 85
13.1 Processing Rules.................................................................................................................. 85
13.2 Service Endpoint Selection Logic........................................................................................... 87
13.3 Selection Element Matching Rules.......................................................................................... 88
13.3.1 Selection Element Match Options.................................................................................... 88
13.3.2 The Match Attribute......................................................................................................... 88
13.3.3 Absent Selection Element Matching Rule......................................................................... 89
13.3.4 Empty Selection Element Matching Rule.......................................................................... 89
13.3.5 Multiple Selection Element Matching Rule........................................................................ 89
13.3.6 Type Element Matching Rules......................................................................................... 89
13.3.7 Path Element Matching Rules.......................................................................................... 90
13.3.8 MediaType Element Matching Rules................................................................................ 92
13.4 Service Endpoint Matching Rules........................................................................................... 92
13.4.1 Service Endpoint Match Options..................................................................................... 92
13.4.2 Select Attribute Match Rule............................................................................................. 92
13.4.3 All Positive Match Rule................................................................................................... 92
13.4.4 Default Match Rule......................................................................................................... 92
13.5 Service Endpoint Selection Rules........................................................................................... 93
13.5.1 Positive Match Rule........................................................................................................ 93
13.5.2 Default Match Rule......................................................................................................... 93
13.6 Pseudocode......................................................................................................................... 93
13.7 Construction of Service Endpoint URIs................................................................................... 95
13.7.1 The append Attribute...................................................................................................... 95
13.7.2 The uric Parameter.......................................................................................................... 96
14 Synonym Verification................................................................................................................ 97
14.1 Redirect Verification.............................................................................................................. 97
14.2 EquivID Verification............................................................................................................... 97
14.3 CanonicalID Verification......................................................................................................... 98
14.3.1 HTTP(S) URI Verification Rules........................................................................................ 99
14.3.2 XRI Verification Rules..................................................................................................... 99
14.3.3 CanonicalEquivID Verification......................................................................................... 99
14.3.4 Verification Status Attributes......................................................................................... 100
14.3.5 Examples..................................................................................................................... 101
15 Status Codes and Error Processing......................................................................................... 106
15.1 Status Elements.................................................................................................................. 106
15.2 Status Codes...................................................................................................................... 106
15.3 Status Context Strings......................................................................................................... 109
15.4 Returning Errors in Plain Text or HTML.................................................................................. 109
15.5 Error Handling in Recursing and Proxy Resolution................................................................. 109
16 Use of HTTP(S)...................................................................................................................... 110
16.1 HTTP Errors........................................................................................................................ 110
16.2 HTTP Headers..................................................................................................................... 110
16.2.1 Caching........................................................................................................................ 110
16.2.2 Location....................................................................................................................... 110
16.2.3 Content-Type................................................................................................................ 110
16.3 Other HTTP Features............................................................................................................ 110
16.4 Caching and Efficiency........................................................................................................ 111
16.4.1 Resolver Caching.......................................................................................................... 111
16.4.2 Synonyms.................................................................................................................... 111
17 Extensibility and Versioning.................................................................................................... 112
17.1 Extensibility........................................................................................................................ 112
17.1.1 Extensibility of XRDs.................................................................................................... 112
17.1.2 Other Points of Extensibility.......................................................................................... 113
17.2 Versioning........................................................................................................................... 113
17.2.1 Version Numbering....................................................................................................... 113
17.2.2 Versioning of the XRI Resolution Specification............................................................... 113
17.2.3 Versioning of Protocols................................................................................................ 114
17.2.4 Versioning of XRDs...................................................................................................... 114
18 Security and Data Protection................................................................................................... 115
18.1 DNS Spoofing or Poisoning................................................................................................ 115
18.2 HTTP Security..................................................................................................................... 115
18.3 SAML Considerations.......................................................................................................... 115
18.4 Limitations of Trusted Resolution......................................................................................... 115
18.5 Synonym Verification........................................................................................................... 116
18.6 Redirect and Ref Management............................................................................................. 116
18.7 Community Root Authorities................................................................................................. 116
18.8 Caching Authorities.............................................................................................................. 116
18.9 Recursing and Proxy Resolution........................................................................................... 116
18.10 Denial-Of-Service Attacks.................................................................................................. 116
A. Acknowledgments.................................................................................................................. 117
B. RelaxNG Schema for XRDS and XRD...................................................................................... 118
C. XML Schema for XRDS and XRD............................................................................................ 121
D. Media Type Definition for application/xrds+xml........................................................................ 125
E. Media Type Definition for application/xrd+xml.......................................................................... 126
F. Example Local Resolver Interface Definition............................................................................. 127
G. Revision History..................................................................................................................... 131
Table of Figures
Figure 1: Four typical scenarios for XRI authority resolution.
Figure 2: Top-level flowchart of XRI resolution phases.
Figure 3: Input processing flowchart.
Figure 4: Output processing flowchart.
Figure 5: Authority resolution flowchart.
Figure 6: XRDS request flowchart.
Figure 7: Redirect and Ref processing flowchart.
Figure 8: Service endpoint (SEP) selection flowchart.
Figure 9: Service endpoint (SEP) selection logic flowchart.
Table of Tables
Table 1: Comparing DNS and XRI resolution architecture.
Table 2: XRIs reserved for XRI resolution.
Table 3: XRIs assigned to identify XRI resolution service types.
Table 4: XML namespace prefixes used in this specification.
Table 5: Media types defined or used in this specification.
Table 6: Parameters for the media types defined in Table 5.
Table 7: The four XRD synonym elements.
Table 8: Input parameters for XRI resolution.
Table 9: Subparameters of the QXRI input parameter.
Table 10: Outputs of XRI resolution.
Table 11: Service Type and Service Media Type values for generic authority resolution.
Table 12: Parsing the first subsegment of an XRI that begins with a global context symbol.
Table 13: Parsing the first subsegment of an XRI that begins with a cross-reference.
Table 14: Examples of the Next Authority URIs constructed using different types of cross-references.
Table 15: Service Type and Service Media Type values for HTTPS trusted authority resolution.
Table 16: Service Type and Service Media Type values for SAML trusted authority resolution.
Table 17: Service Type and Service Media Type values for HTTPS+SAML trusted authority resolution.
Table 18: Service Type and Service Media Type values for proxy resolution.
Table 19: Binding of logical XRI resolution parameters to QXRI query parameters.
Table 20: Example of HXRI components prior to transformation to URI-normal form.
Table 21: Example of HXRI components after transformation to URI-normal form.
Table 22: Example of HXRI components after application of the required encoding rules.
Table 23: Comparison of Redirect and Ref elements.
Table 24: Match options for selection elements.
Table 25: Enumerated values of the global match attribute and corresponding matching rules.
Table 26: Examples of applying the Path element matching rules.
Table 27: Match options for service endpoints.
Table 28: Values of the append attribute and the corresponding QXRI component to append.
Table 29: Error codes for XRI resolution.