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− | == Introduction == | + | [[Image:Higgins_logo_76Wx100H.jpg|right]] |
− | This page describes and defines a Higgins [[ContextId]]. | + | == Version == |
− | See also: [[Context Discovery]] and [[Context Discovery Components]].
| + | This page describes the concept of a [[ContextId]] as used in [[Context Data Model 2.0]]. |
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| == Definition == | | == Definition == |
− | * A [[ContextId]] is a kind of [[Context Correlation]] that identifies an instance of a [[Context]]. | + | * An identifier of a [[Context]] |
− | * A [[ContextId]] MUST have a single value | + | * A ''Context UDI'' as defined in [http://www.azigo.com/udi/udi-syntax.html UDI Syntax] |
− | * The single value of a [[ContextId]] MUST be a [[ContextIdDatatype]]
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− | == Details ==
| + | [[Category:Context Data Model 2.0]] |
− | * The value of a [[ContextId]] must directly or indirectly (e.g. by resolution) provide sufficient information to identify 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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− | == ContextId and IdAS ==
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− | * If two [[ContextId]]'s values are equal, they refer to the same underlying [[Context]], although not necessarily the same [[Context]] "container" instance returned by IdAS. 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.
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− | * 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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− | == Details ==
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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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− | Some [[ContextId]]s are not resolvable to a [[Context]] instance. Most [[Context]]s are not abstract. Using a network (or local) data access service their [[ContextId]]s are resolvable to data objects that are instantiated and managed by [[Context Provider]] plug-ins.
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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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− | * [[EntityId]]
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− | * [[LocalId]]
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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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