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Difference between revisions of "ContextId"

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== Introduction ==
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[[Image:Higgins_logo_76Wx100H.jpg|right]]
This page describes and defines a Higgins [[ContextId]].
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== Version ==
See also: [[Context Discovery]] and [[Context Discovery Components]].
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This page describes the concept of a [[ContextId]] as used in [[Context Data Model 2.0]].
  
 
== Definition ==
 
== Definition ==
A '''ContextId''' is a URI or XRI that identifies one [[Context]].
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* An identifier of a [[Context]]  
* A [[ContextId]] MUST conform to the ABNF defined below.
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* A ''Context UDI'' as defined in [http://www.azigo.com/udi/udi-syntax.html UDI Syntax]
* A [[ContextId]] must directly or indirectly (e.g. by resolution) provide sufficient information to both identify and open a [[Context]]. See the ''Context Discovery with a ContextId'' heading below.
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* Two different [[ContextId]]s may refer to the same [[Context]].
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* If two [[ContextId]]s are equal, they refer to the same underlying [[Context]] dataset, although not necessarily the same [[Context]] "container" instance. This means that, as a requester of information, different [[Digital Identity|Digital Identities]] may see different subsets of the [[Context]] based on the authorization passed in during authentication. A given [[ContextId]] may be used against multiple [[Context Provider]]s to produce the same [[Context]] (although, as mentioned, different [[Context]] instances).
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* The [[Identity Attribute Service (IdAS)]] can be used as a service to access a [[Context]] given a [[ContextId]]
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== Syntax ==
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[[Category:Context Data Model 2.0]]
The following [http://en.wikipedia.org/wiki/Augmented_Backus-Naur_form ABNF] defines a Higgins [[ContextId]]. All rules not defined in this ABNF are defined in the [http://wiki.oasis-open.org/xri/XriCd02/Xri2dot0Abnf ABNF for XRI 2.0] (which includes the IRI ABNF from [http://www.ietf.org/rfc/rfc3987.txt RFC 3987]) except:
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* '''xri2-authority''' and '''xri2-subseg''' are the '''xri-authority''' and '''xri-subset''' rules defined in the [http://wiki.oasis-open.org/xri/XriCd02/Xri2dot0Abnf ABNF for XRI 2.0]
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* '''xri3-authority''' and '''xri3-subseg''' are the '''xri-authority''' and '''xri-subset''' rules defined in the [http://wiki.oasis-open.org/xri/XriThree/SyntaxAbnf proposed ABNF for XRI 3.0]
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<pre>
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contextId          = contextURI / contextXRI
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contextURI        = contextfileURI / contexthttpURI
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contextfileURI    = [ "file://" ] ipath-abempty descriptor-ext
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descriptor-ext    = ".xrds" / ".xdi"                                      ;see note 1
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contexthttpURI    = ( "http://" / "https://" ) iauthority
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                    ipath-abempty [ descriptor-ext ] [ "?" iquery ]
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contextXRI        = contextQXRI /                                        ;see note 2
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                    contextHXRI                                          ;see note 3
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contextQXRI        = ( [ "xri://" ] xri2-contextQXRI ) /
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                    ( [ "xri:" ] xri3-contextQXRI )
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xri2-contextQXRI  = xri2-authority [ "/($context)" *xri2-subseg ]
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xri3-contextQXRI  = xri3-authority [ "/$context" *xri3-subseg ]
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contextHXRI        = proxy-URI "/" (xri2-contextQXRI / xri3-contextQXRI )
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proxy-URI          = ( "http://" / "https://" ) proxy-reg-name
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proxy-reg-name    = "xri." ireg-name
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</pre>
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Notes:
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# ".xrds" and ".xdi" are formats designed expressly for discovery and description of resources using HTTP(S) URIs and/or XRIs. XRDS format is defined by [http://www.oasis-open.org/committees/download.php/24286/xri-resolution-v2.0-wd-11-ed-02.doc XRI Resolution Working 2.0]. XDI format is being defined by the [http://www.oasis-open.org/committees/xdi OASIS XDI Technical Committee]. Other resource description file types can be supported by extending this ABNF rule.
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# QXRI (Query XRI) is an XRI in URI-normal form without the "xri://" prefix (XRI 2.0) or "xri:" prefix (XRI 3.0). See Section 11.2 of [http://docs.oasis-open.org/xri/2.0/specs/cd02/xri-resolution-V2.0-cd-02.pdf XRI Resolution 2.0].
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# 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 6 of [http://docs.oasis-open.org/xri/2.0/specs/cd02/xri-resolution-V2.0-cd-02.pdf XRI Resolution 2.0].
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== Examples ==
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=== contextURI ===
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==== contextfileURI ====
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file://system/config/openid.xrds
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file://system/config/openid.xdi
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file://system/config/ldap.xrds
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file://system/config/ldap.xdi
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==== contexthttpURI ====
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http://example.com
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https://example.com
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http://example.com#msabadello
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https://example.com#msabadello
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http://example.com/higgins/openid.xrds
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https://example.com/higgins/openid.xdi
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http://example.com/higgins/ldap.xrds#msabadello
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https://example.com/higgins/ldap.xdi#msabadello
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=== ContextQXRI ===
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==== contextQXRI – XRI 2.0 Form ====
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=drummond
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=drummond/($context)
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=drummond/($context)*($openid)
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=drummond/($context)*($ldap)
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=!F83.62B1.44F.2813
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=!F83.62B1.44F.2813/($context)*($openid)
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=!F83.62B1.44F.2813/($context)*($ldap)
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=drummond*mom
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=drummond*mom/($context)*($openid)
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=drummond*mom/($context)*($ldap)
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@example
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@example/($context)
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@example/($context)*($openid)
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@example/($context)*($ldap)
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@free*example
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@free*example/($context)*($openid)
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@free*example/($context)*($ldap)
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==== contextQXRI – Proposed XRI 3.0 Form ====
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=drummond
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=drummond/$context
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=drummond/$context$openid
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=drummond/$context$ldap
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=!F83.62B1.44F.2813
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=!F83.62B1.44F.2813/$context$openid
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=!F83.62B1.44F.2813/$context$$ldap
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=drummond*mom
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=drummond*mom/$context$openid
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=drummond*mom/$context$ldap
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@example
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@example/$context
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@example/$context$openid
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@example/$context$ldap
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@free*example
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@free*example/$context$openid
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@free*example/$context$ldap
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=== contextHXRI ===
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A contextHXRI is a ContextQXRI that uses an HXRI proxy resolver prefix. "xri.net" is a public HXRI proxy resolver operated by XDI.org. All others are examples.
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==== contextHXRI – XRI 2.0 Form ====
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http://xri.net/=drummond
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http://xri.net/=drummond/($context)
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https://xri.net/=drummond/($context)*($openid)
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https://xri.net/=drummond*mom/($context)*($openid)
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http://xri.example.com/@example/($context)*($openid)
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http://xri.example.com/@free*example/($context)*($openid)
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https://xri.example.org/@1000.a1b2.c3d4.9999!1234/($context)*($ldap)
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==== contextHXRI – Proposed XRI 3.0 Form ====
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http://xri.net/=drummond
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http://xri.net/=drummond/$context
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https://xri.net/=drummond/$context$openid
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https://xri.net/=drummond*mom/$context$openid
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http://xri.example.com/@example/$context$openid
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http://xri.example.com/@example*free/$context$openid
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https://xri.example.org/@1000.a1b2.c3d4.9999!1234/$context$ldap
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== Context Discovery Rules ==
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A key property of a [[ContextId]] is that it can be resolved into the metadata necessary open a [[Context]]. The complete process for doing this is described in [[Context Discovery]]. Following are the discovery rules that apply to each form of ContextId.
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=== contextURI Discovery ===
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Since URIs do not offer the structured identifier features of XRIs, they must resolve directly to an XRDS or XDI document containing the Higgins context configuration metadata for a specific context type.
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==== contextfileURI ====
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# Open the identified file.
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# For an XRDS file, select the highest priority service endpoint that conforms to the [[Higgins XRDS Service Endpoint]] requirements.
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# For an XDI X3 file, parse the Higgins context configuration metadata from the X3 document as described in [[Higgins XDI Context Reference]].
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==== contexthttpURI ====
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# Resolve the URI to a discovery document as specified in Section 6 of [http://docs.oasis-open.org/xri/2.0/specs/cd02/xri-resolution-V2.0-cd-02.pdf XRI Resolution 2.0].
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## If the contexthttpURI ends in the context descriptor extension '''.xrds''' for an XRDS document, use the MIME type '''application/xrds+xml'''.
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## If the contexthttpURI ends in the context descriptor extension '''.xdi''' for an XDI document, use the MIME type '''text/x3'''.
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## If the contexthttpURI does not end in a context descriptor extension, use either or both of these MIME types as preferred in content negotiation with the server.
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# If the MIME type of the discovery document is '''application/xrds+xml''', select the highest priority service endpoint that conforms to the [[Higgins XRDS Service Endpoint]] requirements.
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# If the MIME type is '''text/x3''', parse the Higgins context configuration metadata from the X3 document as described in [[Higgins XDI Context Reference]].
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=== contextXRI Discovery ===
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Since XRIs are abstract structured identifiers intended designed explicitly for resource discovery and description, they offer more flexiblity in the discovery process.
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==== Using XRDS ====
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# Resolve the authority component of the XRI as specified in [http://docs.oasis-open.org/xri/2.0/specs/cd02/xri-resolution-V2.0-cd-02.pdf XRI Resolution 2.0]. Trusted resolution is RECOMMENDED.
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# From this XRDS document, select the Higgins service endpoint as defined in Section 13 of [http://docs.oasis-open.org/xri/2.0/specs/cd02/xri-resolution-V2.0-cd-02.pdf XRI Resolution 2.0]. Note that this provides a number of ways for ContextXRI authors to control service endpoint selection. Using the path component of the XRI to match a [[Higgins XRDS Service Endpoint]] is RECOMMENDED.
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# Parse the Higgins context metadata as defined in [[Higgins XRDS Service Endpoint]].
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==== Using XDI ====
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# Resolution of the authority component of the XRI may use either XRDS resolution or XDI context discovery.
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## For XRDS resolution, follow the same steps as described above, except that in the final XRDS document, the highest priority SEP of type '''xri://$xdi''' MUST be selected, and an XDI X3 document MUST be requested from that service endpoint URI.
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## For XDI context discovery, resolve the authority component of the XRI as specified in the XDI Contexts section of [http://wiki.oasis-open.org/xdi/XdiRdfModel XDI RDF Model]] document.
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# In both cases, from the final XDI document, parse the XDI context description as defined in [[Higgins XDI Context Reference]].
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== Relationship to OpenID ==
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Any OpenID 2.0 identifier as defined by [http://openid.net/specs/openid-authentication-2_0.html OpenID Authentication 2.0] may function as a Higgins [[ContextId]]. OpenID 2.0 supports both URLs and XRIs. All of the examples of contexthttpURI and contextXRI above are valid OpenID 2.0 identifiers.
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The only caveat to keep in mind is that if an OpenID 2.0 URL is used as a Higgins [[ContextId]], the XRDS or XDI document to which it resolves must EITHER contain:
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* Only one XRDS service endpoint or XDI context reference describing the target [[Context]], OR
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* The consuming application must know how to select the XRDS service endpoint or XDI context reference it requires (i.e., it must know which Higgins [[Context Type]] it is seeking).
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== Open Issues ==
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# 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.
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== See Also ==
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* [[SubjectId]]
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* [[Relation]]
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* [[Context Discovery]]
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* [[Context Discovery Components]]
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* [[Higgins XRDS Service Endpoint]]
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* [[Higgins XDI Context Reference]]
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* [[Concepts]]
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== Links ==
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* [http://eclipse.org/higgins Higgins Home]
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Latest revision as of 11:35, 31 May 2021

Higgins logo 76Wx100H.jpg

Version

This page describes the concept of a ContextId as used in Context Data Model 2.0.

Definition

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