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Revision as of 17:30, 23 January 2008 by (Talk | contribs) (ABNF)


This page describes and defines a Higgins ContextId. See also: Context Discovery and Context Discovery Components.


  • A ContextId is a URI or XRI that identifies one Context.
  • A ContextId MUST conform to the ABNF defined below.
  • ContextIds either directly or indirectly (e.g. by resolution) provide sufficient information to identify a Context.
  • Two different ContextIds may refer to the same Context.
  • If two ContextIds are equal, they refer to the same underlying Context dataset, although not necessarily the same Context "container" instance, and, based on the authorization of the Digital Identity passed in during authentication, may only be permitted to see a subset of its contents.
  • A given ContextId may be used against multiple Context Factories to produce the same Context (although, as mentioned, different Context instances).
  • The Identity Attribute Service (IdAS) can be used as a service to access a Context given a ContextId


Note that this ABNF also defines a Higgins SubjectId and Subject Relation.

Rules not defined in this ABNF are defined in the ABNF for XRI 2.0 (which includes the IRI ABNF from RFC 3987).

contextId          = contextURI / contextXRI
contextURI         = contextfileURI / contexthttpURI
contextfileURI     = [ "file://" ] ipath-abempty descriptor-ext
descriptor-ext     = ".xrds" / ".xdi"                                     ;see note 1
contexthttpURI     = ( "http://" / "https://" ) iauthority
                     ipath-abempty [ descriptor-ext ] [ "?" iquery ]
contextXRI         = [ "xri://" ] contextQXRI /                           ;see note 2
                     contextHXRI                                          ;see note 3
contextQXRI        = xri-authority ( "/($context) [ "*" / "!" ] / "/$context" ) [ xri-segment ]
contextHXRI        = proxy-resolver "/" contextQXRI
proxy-resolver     = ( "http://" / "https://" ) proxy-reg-name
proxy-reg-name     = "xri." ireg-name
subjectId          = ifragment / xri-segment
relation           = relationURI / relationXRI
relationURI        = contextURI [ "#" subjectId ]
relationXRI        = contextXRI [ "//" subjectId ]


  1. These are the first two file types are designed expressly for discovery and description of resources using HTTP(S) URIs and/or XRIs. XRDS format is defined by XRI Resolution Working 2.0. XDI format is being defined by the OASIS XDI Technical Committee. Future file types can be supported by extending this ABNF rule.
  2. QXRI (Query XRI) is an XRI in URI-normal form without the "xri://" prefix. See XRI Resolution 2.0.
  3. HXRI (HTTP(S) XRI) is the format for encapsulating an XRI within an HTTP(S) URI for purposes of resolution by an XRI proxy resolver. See section 8 of XRI Resolution 2.0.



A ContextId in ContextURI form can be either a file or HTTP(S) URI. In either case it must end with either ".xrds" or ".xdi".



A ContextQXRI (Query XRI) is a pure XRI in XRI-normal form that does not include the "xri://" prefix.



A contextHXRI is a ContextQXRI that uses an HXRI proxy resolver prefix. "" is a public HXRI proxy resolver operated by All others are examples.$context+openid$context+openid$context+ldap

Open Issues

  1. Should the contextId ABNF support IRI (Internationalized Resource Identifiers) and not just URIs? Note that the ABNF above uses IRI rules; this needs to be changed if only URIs will be supported.
  2. Do we need a method in IdAS to test that two given ContextIds actually resolve to the same Context?

See Also


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