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ContextId

Revision as of 16:18, 29 January 2008 by Drummond.reed.cordance.net (Talk | contribs) (contexthttpURI: backed out last change - wrong page)

Introduction

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

Definition

A ContextId is a URI or XRI that identifies one Context.

  • A ContextId MUST conform to the ABNF defined below.
  • 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.
  • 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. This means that, as a requester of information, different 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 Providers 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

Syntax

The following ABNF defines a Higgins ContextId. All rules not defined in this ABNF are defined in the ABNF for XRI 2.0 (which includes the IRI ABNF from RFC 3987) except:

  • xri2-authority and xri2-subseg are the xri-authority and xri-subset rules defined in the ABNF for XRI 2.0
  • xri3-authority and xri3-subseg are the xri-authority and xri-subset rules defined in the proposed ABNF for XRI 3.0
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         = contextQXRI /                                         ;see note 2
                     contextHXRI                                           ;see note 3
contextQXRI        = ( [ "xri://" ] xri2-contextQXRI ) / 
                     ( [ "xri:" ] xri3-contextQXRI )
xri2-contextQXRI   = xri2-authority [ "/($context)" *xri2-subseg ] 
xri3-contextQXRI   = xri3-authority [ "/$context" *xri3-subseg ] 
contextHXRI        = proxy-URI "/" (xri2-contextQXRI / xri3-contextQXRI )
proxy-URI          = ( "http://" / "https://" ) proxy-reg-name
proxy-reg-name     = "xri." ireg-name

Notes:

  1. ".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 XRI Resolution Working 2.0. XDI format is being defined by the OASIS XDI Technical Committee. Other resource description 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 (XRI 2.0) or "xri:" prefix (XRI 3.0). See Section 11.2 of 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 6 of XRI Resolution 2.0.

Examples

contextURI

contextfileURI

file://system/config/openid.xrds
file://system/config/openid.xdi
file://system/config/ldap.xrds
file://system/config/ldap.xdi

contexthttpURI

http://example.com
https://example.com
http://example.com
https://example.com
http://example.com/higgins/openid.xrds
https://example.com/higgins/openid.xdi
http://example.com/higgins/ldap.xrds
https://example.com/higgins/ldap.xdi

ContextQXRI

contextQXRI – XRI 2.0 Form

=drummond
=drummond/($context)
=drummond/($context)*($openid)
=drummond/($context)*($ldap)
=!F83.62B1.44F.2813
=!F83.62B1.44F.2813/($context)*($openid)
=!F83.62B1.44F.2813/($context)*($ldap)
=drummond*mom
=drummond*mom/($context)*($openid)
=drummond*mom/($context)*($ldap)
@example
@example/($context)
@example/($context)*($openid)
@example/($context)*($ldap)
@free*example
@free*example/($context)*($openid)
@free*example/($context)*($ldap)

contextQXRI – Proposed XRI 3.0 Form

=drummond
=drummond/$context
=drummond/$context$openid
=drummond/$context$ldap
=!F83.62B1.44F.2813
=!F83.62B1.44F.2813/$context$openid
=!F83.62B1.44F.2813/$context$$ldap
=drummond*mom
=drummond*mom/$context$openid
=drummond*mom/$context$ldap
@example
@example/$context
@example/$context$openid
@example/$context$ldap
@free*example
@free*example/$context$openid
@free*example/$context$ldap

contextHXRI

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.

contextHXRI – XRI 2.0 Form

http://xri.net/=drummond
http://xri.net/=drummond/($context)
https://xri.net/=drummond/($context)*($openid)
https://xri.net/=drummond*mom/($context)*($openid)
http://xri.example.com/@example/($context)*($openid)
http://xri.example.com/@free*example/($context)*($openid)
https://xri.example.org/@1000.a1b2.c3d4.9999!1234/($context)*($ldap)

contextHXRI – Proposed XRI 3.0 Form

http://xri.net/=drummond
http://xri.net/=drummond/$context
https://xri.net/=drummond/$context$openid
https://xri.net/=drummond*mom/$context$openid
http://xri.example.com/@example/$context$openid
http://xri.example.com/@example*free/$context$openid
https://xri.example.org/@1000.a1b2.c3d4.9999!1234/$context$ldap

Context Discovery Rules

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.

contextURI Discovery

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.

contextfileURI

  1. Open the identified file.
  2. For an XRDS file, select the highest priority service endpoint that conforms to the Higgins XRDS Service Endpoint requirements.
  3. For an XDI X3 file, parse the Higgins context configuration metadata from the X3 document as described in Higgins XDI Context Reference.

contexthttpURI

  1. Resolve the URI to a discovery document as specified in Section 6 of XRI Resolution 2.0.
    1. If the contexthttpURI ends in the context descriptor extension .xrds for an XRDS document, use the MIME type application/xrds+xml.
    2. If the contexthttpURI ends in the context descriptor extension .xdi for an XDI document, use the MIME type text/x3.
    3. 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.
  2. 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.
  3. If the MIME type is text/x3, parse the Higgins context configuration metadata from the X3 document as described in Higgins XDI Context Reference.

contextXRI Discovery

Since XRIs are abstract structured identifiers intended designed explicitly for resource discovery and description, they offer more flexiblity in the discovery process.

Using XRDS

  1. Resolve the authority component of the XRI as specified in XRI Resolution 2.0. Trusted resolution is RECOMMENDED.
  2. From this XRDS document, select the Higgins service endpoint as defined in Section 13 of 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.
  3. Parse the Higgins context metadata as defined in Higgins XRDS Service Endpoint.

Using XDI

  1. Resolution of the authority component of the XRI may use either XRDS resolution or XDI context discovery.
    1. 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.
    2. For XDI context discovery, resolve the authority component of the XRI as specified in the XDI Contexts section of XDI RDF Model] document.
  2. In both cases, from the final XDI document, parse the XDI context description as defined in Higgins XDI Context Reference.

Relationship to OpenID

Any OpenID 2.0 identifier as defined by 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.

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:

  • Only one XRDS service endpoint or XDI context reference describing the target Context, OR
  • 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).

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.

See Also

Links

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