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<articleinfo>
	<title>Extensible Resource Descriptor (XRD) Version 1.0</title>

	<releaseinfo role="cvs">
		$Id: xrd-1.0.xml 198 2010-03-24 20:34:07Z willnorris $
	</releaseinfo>

	<productname>&document-id;</productname>

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	<releaseinfo role="committee">
		<ulink url="http://www.oasis-open.org/committees/xri/">OASIS Extensible Resource Identifier (XRI) TC</ulink>
	</releaseinfo>

	<authorgroup>
		<othercredit>
			<firstname>Peter</firstname><surname>Davis</surname>
			<affiliation>
				<orgname>NeuStar Inc.</orgname>
			</affiliation>
		</othercredit>
		<othercredit>
			<firstname>Drummond</firstname><surname>Reed</surname>
			<affiliation>
				<orgname>XDI.org</orgname>
			</affiliation>
		</othercredit>
		<editor>
			<firstname>Eran</firstname><surname>Hammer-Lahav</surname>
		</editor>
		<editor>
			<firstname>Will</firstname><surname>Norris</surname>
			<affiliation>
				<orgname>Internet2</orgname>
			</affiliation>
		</editor>
	</authorgroup>

	<pubdate>&pubdate;</pubdate>

	<copyright>
		<year>2010</year>
		<holder>OASIS Open, Inc. All Rights Reserved.</holder>
	</copyright>

	<legalnotice role="related">
		<title>Related Work</title>

		<para>This specification replaces or supersedes:</para>
		<itemizedlist spacing="compact">
			<listitem>
				<para>
					<ulink url="http://docs.oasis-open.org/xri/2.0/specs/xri-resolution-V2.0.html">
						Extensible Resource Identifier (XRI) Resolution Version 2.0, Committee Specification 01,
						April 2008
					</ulink>
				</para>
			</listitem>
		</itemizedlist>
	</legalnotice>

	<legalnotice role="namespaces">
		<title>Declared XML Namespace</title>
		<itemizedlist spacing="compact">
			<listitem>
				<para>
					<ulink url="http://docs.oasis-open.org/ns/xri/xrd-1.0" />
				</para>
			</listitem>
		</itemizedlist>
	</legalnotice>

	<abstract>
		<para>This document defines XRD, a simple generic format for describing and discovering resources.</para>
	</abstract>

	<legalnotice role="status">
		<title>Status</title>

		<para>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 current location noted above for possible later revisions of this
			document. This document is updated periodically on no particular schedule.</para>
		<para>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 <ulink url="http://www.oasis-open.org/committees/xri" />.
		</para>
		<para>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
			(<ulink url="http://www.oasis-open.org/committees/xri/ipr.php" />).
		</para>
		<para>The non-normative errata page for this specification is located at
			<ulink url="http://www.oasis-open.org/committees/xri" />.</para>
	</legalnotice>

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		<title>Notices</title>

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</articleinfo>

<section id="introduction">
	<title>Introduction</title>

	<para>
		This document defines XRD (Extensible Resource Descriptor), a simple generic format for describing resources.
		Resource descriptor documents provide machine-readable information about resources (resource metadata) for the
		purpose of promoting interoperability. They also assist in interacting with unknown resources that support
		known interfaces.
	</para>

	<para>
		For example, a web page about an upcoming meeting can provide in its descriptor document the location of the
		meeting organizer's free/busy information to potentially negotiate a different time.  The descriptor for a
		social network profile page can identify the location of the user's address book as well as accounts on other
		sites.  A web service implementing an API protocol can advertise which of the protocol's optional components
		are supported.
	</para>

	<section id="terminology">
		<title>Terminology</title>

		<para>
			The key words <phrase role="keyword">must</phrase>, <phrase role="keyword">must not</phrase>,
			<phrase role="keyword">required</phrase>, <phrase role="keyword">shall</phrase>,
			<phrase role="keyword">shall not</phrase>, <phrase role="keyword">should</phrase>,
			<phrase role="keyword">should not</phrase>, <phrase role="keyword">recommended</phrase>,
			<phrase role="keyword">may</phrase>, and <phrase role="keyword">optional</phrase> in this document are to
			be interpreted as described in <xref linkend="rfc2119"/>.
		</para>
	</section>

	<section id="normative.references">
		<title>Normative References</title>

		<bibliography>
			<title />

			<bibliodiv>

				<bibliomixed id="excl-c14n">
					<abbrev>Exclusive Canonicalization</abbrev> J. Boyer, D. Eastlake, J. Reagle.
					<citetitle><ulink url="http://www.w3.org/TR/xml-exc-c14n/">Exclusive XML Canonicalization</ulink></citetitle>.
					W3C Recommendation, 2002.
				</bibliomixed>

				<bibliomixed id="rfc2119">
					<abbrev>RFC 2119</abbrev> S. Bradner.
					<citetitle><ulink url="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</ulink></citetitle>.
					IETF, 1997.
				</bibliomixed>

				<bibliomixed id="rfc3023">
					<abbrev>RFC 3023</abbrev> M. Murata, S. St. Laurent, D. Kohn.
					<citetitle><ulink url="http://tools.ietf.org/html/rfc3023">XML Media Types</ulink></citetitle>.
					IETF, 2001.
				</bibliomixed>

				<bibliomixed id="rfc3986">
					<abbrev>RFC 3986</abbrev> T. Berners-Lee, R. Fielding, L. Masinter.
					<citetitle><ulink url="http://tools.ietf.org/html/rfc3986">Uniform Resource Identifier (URI): Generic Syntax</ulink></citetitle>.
					IETF, 2005.
				</bibliomixed>

				<bibliomixed id="rfc4288">
					<abbrev>RFC 4288</abbrev> N. Freed, J. Klensin.
					<citetitle><ulink url="http://tools.ietf.org/html/rfc4288">Media Type Specifications and Registration Procedures</ulink></citetitle>.
					IETF, 2005.
				</bibliomixed>

				<bibliomixed id="web-linking">
					<abbrev>Web Linking</abbrev> M. Nottingham.
					<citetitle><ulink url="http://tools.ietf.org/html/draft-nottingham-http-link-header">Web Linking</ulink></citetitle>.
					IETF Draft, 2009.
				</bibliomixed>

				<bibliomixed id="xml">
					<abbrev>XML 1.0</abbrev> T. Bray, J. Paoli, C. Sperberg-McQueen, E. Maler, F. Yergeau.
					<citetitle><ulink url="http://www.w3.org/TR/REC-xml/">Extensible Markup Language (XML) 1.0</ulink></citetitle>.
					W3 Recommendation, 2008.
				</bibliomixed>

				<bibliomixed id="xml-schema">
					<abbrev>XML Schema</abbrev> H. Thompson, D. Beech, M. Maloney, N. Mendelsohn.
					<citetitle><ulink url="http://www.w3.org/TR/xmlschema-1/">XML Schema Part 1: Structures Second Edition</ulink></citetitle>.
					W3C Recommendation, 2004.
				</bibliomixed>

				<bibliomixed id="schema-datatypes">
					<abbrev>XML Schema Datatypes</abbrev> P. Biron, A. Malhotra.
					<citetitle><ulink url="http://www.w3.org/TR/xmlschema-2/">XML Schema Part 2: Datatypes Second Edition</ulink></citetitle>.
					W3 Recommendation, 2004.
				</bibliomixed>

				<bibliomixed id="xml-sig">
					<abbrev>XML Signature</abbrev> D. Eastlake, J. Reagle, D. Solo, F. Hirsch, T. Roessler.
					<citetitle><ulink url="http://www.w3.org/TR/xmldsig-core/">XML Signature Syntax and Processing</ulink></citetitle>.
					W3 Recommendation, 2008.
				</bibliomixed>

				<bibliomixed id="xml-id">
					<abbrev>xml:id</abbrev> J. Marsh, D. Veillard, N. Walsh.
					<citetitle><ulink url="http://www.w3.org/TR/xml-id/">xml:id</ulink></citetitle>.
					W3 Recommendation, 2005.
				</bibliomixed>

			</bibliodiv>

		</bibliography>
	</section>

	<section id="non-normative.references">
		<title>Non-Normative References</title>

		<bibliography>
			<title />

			<bibliodiv>
				<bibliomixed id="atom">
					<abbrev>Atom 1.0</abbrev> M. Nottingham, R. Sayre.
					<citetitle><ulink url="http://tools.ietf.org/html/rfc4287">The Atom Syndication Format</ulink></citetitle>.
					IETF, 2005.
				</bibliomixed>

				<bibliomixed id="html-4">
					<abbrev>HTML 4.01</abbrev> D. Raggett, A. Le Hors, I. Jacobs.
					<citetitle><ulink url="http://www.w3.org/TR/html401/">HTML 4.01 Specification</ulink></citetitle>.
					W3C Recommendation, 1999.
				</bibliomixed>

				<bibliomixed id="xri-resolution-2">
					<abbrev>XRI Resolution 2.0</abbrev> G. Wachob, D. Reed, L. Chasen, W. Tan, S. Churchill
					<citetitle><ulink url="http://docs.oasis-open.org/xri/2.0/specs/xri-resolution-V2.0.html">Extensible Resource Identifier (XRI) Resolution V2.0</ulink></citetitle>.
					OASIS, 2008.
				</bibliomixed>
			</bibliodiv>

		</bibliography>

	</section>

	<section id="schema">
		<title>Schema Organization and Namespaces</title>

		<para>
			The XRD document structure is defined in a schema associated with the following XML namespace:
			<programlisting>http://docs.oasis-open.org/ns/xri/xrd-1.0</programlisting>
		</para>

		<para>
			The schema for <xref linkend="xml" /> (the "xml:" namespace), which is associated with the following XML
			namespace, is imported into the XRD schema:
			<programlisting>http://www.w3.org/XML/1998/namespace</programlisting>
		</para>

		<para>
			The following <xref linkend="xml-schema" /> fragment defines the XML namespaces and other header
			information for the XRD schema:

			<programlisting><![CDATA[<schema targetNamespace="http://docs.oasis-open.org/ns/xri/xrd-1.0"
  xmlns="http://www.w3.org/2001/XMLSchema"
  xmlns:xrd="http://docs.oasis-open.org/ns/xri/xrd-1.0"
  elementFormDefault="unqualified"
  attributeFormDefault="unqualified"
  blockDefault="substitution"
  version="1.0">

    <import namespace="http://www.w3.org/XML/1998/namespace"
        schemaLocation="http://www.w3.org/2001/xml.xsd"/>

    <annotation>
        <documentation>
            Document identifier: xrd-schema-1.0
            Location: http://docs.oasis-open.org/xri/xrd/v1.0/
        </documentation>
    </annotation>
...
</schema>
]]></programlisting>
		</para>

		<para>
			The location of the normative XML Schema file for an XRD document as defined by this specification is:
			<literal><ulink url="&this-file;.xsd" /></literal>.  The following URI will always reference the latest
			version of this file: <ulink url="&latest-file;.xsd"><literal>&latest-file;.xsd</literal></ulink>.
		</para>

	</section>


	<section id="types">
		<title>Common Data Types</title>

		<section id="types.string">
			<title>String Values</title>

			<para>
				All XRD string values have or extend the type <sgmltag class="attvalue">xs:string</sgmltag>, which is
				built in to the W3C <xref linkend="schema-datatypes" /> specification. Unless otherwise noted in this
				specification or particular profiles, all strings in XRD documents <phrase role="keyword">must</phrase>
				consist of at least one non-whitespace character (whitespace is defined in section 2.3 of
				<xref linkend="xml" />).
			</para>

			<para>
				The following schema fragment defines the <sgmltag>xrd:string</sgmltag> complex type, which extends
				<sgmltag>xs:string</sgmltag> to allow for arbitrary attributes (see
				<xref linkend="schema.extension" />):

				<programlisting><![CDATA[<complexType name="string">
    <simpleContent>
        <extension base="string">
            <anyAttribute namespace="##other" processContents="lax"/>
        </extension>
    </simpleContent>
</complexType>]]></programlisting>
			</para>
		</section>

		<section id="types.uri">
			<title>URI Values</title>

			<para>
				All XRD URI reference values have or extend the type <sgmltag class="attvalue">xs:anyURI</sgmltag>,
				which is built in to the W3C <xref linkend="schema-datatypes" /> specification. Unless otherwise noted
				in this specification or particular profiles, all URIs in XRD documents
				<phrase role="keyword">must</phrase> consist of at least one non-whitespace character (whitespace is
				defined in section 2.3 of <xref linkend="xml" />).
			</para>

			<para>
				The following schema fragment defines the <sgmltag>xrd:anyURI</sgmltag> complex type, which extends
				<sgmltag>xs:anyURI</sgmltag> to allow for arbitrary attributes (see
				<xref linkend="schema.extension" />):

				<programlisting><![CDATA[<complexType name="anyURI">
    <simpleContent>
        <extension base="anyURI">
            <anyAttribute namespace="##other" processContents="lax"/>
        </extension>
    </simpleContent>
</complexType>]]></programlisting>
			</para>
		</section>

		<section id="types.time">
			<title>Time Values</title>

			<para>
				All XRD time values have the type <sgmltag class="attvalue">xs:dateTime</sgmltag>, which is built in
				to the W3C <xref linkend="schema-datatypes" /> specification. Time values
				<phrase role="keyword">must</phrase> be represented with the UTC designator 'Z'. XRD providers
				<phrase role="keyword">must not</phrase> generate time instants that specify leap seconds.
			</para>
		</section>
	</section>

</section>

<section id="document.structure">
	<title>XRD Document Structure</title>

	<para>
		XRD provides a simple and extensible XML format for describing a resource. An XRD document may describe the
		properties of the resource itself, as well as the relations the resource has with other resources.  XRD
		builds directly on the typed link relations framework defined by <xref linkend="web-linking" />, and used by
		<xref linkend="html-4" />, <xref linkend="atom" />, and other protocols.
	</para>

	<para>
		An XRD document <phrase role="keyword">must</phrase> (a) be a well-formed XML document as defined by
		<xref linkend="xml" /> with a root element of
		<link linkend="element.xrd"><sgmltag class="starttag">XRD</sgmltag></link>,
		(b) validate against the normative XRD schema identified in <xref linkend="schema" />, and (c) adhere to the
		additional syntactic constraints defined by <xref linkend="types" /> and this section.
	</para>

	<para>
		The XRD schema defines only the elements necessary to support the most common use cases, with the
		explicit intention that applications will extend XRD as defined in <xref linkend="extensibility" />
		to include other metadata about the resources and links they describe.
	</para>

	<section id="element.xrd">
		<title>Element <sgmltag class="starttag">XRD</sgmltag></title>
		<para>
			The <sgmltag class="starttag">XRD</sgmltag> element encapsulates the entire resource descriptor.  It
			contains the following attributes and elements:

			<variablelist>

				<varlistentry>
					<term><sgmltag class="attribute">xml:id</sgmltag> [Optional]</term>
					<listitem>
						<para>
							This attribute, of type <sgmltag class="attvalue">xs:ID</sgmltag>, is defined by
							<xref linkend="xml-id" />.  It provides a unique identifier for this XRD, and is used
							as a <link linkend="signature.references">signature reference</link>.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry>
					<term><sgmltag class="starttag">Expires</sgmltag> [Zero or One]</term>
					<listitem>
						<para>
							Specifies when this document expires. See <xref linkend="element.expires" />.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry>
					<term><sgmltag class="starttag">Subject</sgmltag> [Zero or One]</term>
					<listitem>
						<para>
							Provides the identifier of the resource described by this XRD.  See
							<xref linkend="element.subject" />.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry>
					<term><sgmltag class="starttag">Alias</sgmltag> [Zero or More]</term>
					<listitem>
						<para>
							Provides an additional identifier for the resource described by this XRD.  See
							<xref linkend="element.alias" />.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry>
					<term><sgmltag class="starttag">Property</sgmltag> [Zero or More]</term>
					<listitem>
						<para>
							Declares a property of the resource described by this XRD. See
							<xref linkend="element.property" />.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry>
					<term><sgmltag class="starttag">Link</sgmltag> [Zero or More]</term>
					<listitem>
						<para>
							Identifies another resource which is related to the resource described by this XRD, and
							describes the semantics of that relation.  See <xref linkend="element.link" />.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry>
					<term><sgmltag class="starttag">ds:Signature</sgmltag> [Zero or More]</term>
					<listitem>
						<para>
							This XML Signature, included from the <xref linkend="xml-sig" /> schema, protects the
							integrity of the document, as described in <xref linkend="signature" />.
						</para>

						<para>
							Although <xref linkend="xml-sig" /> allows a single document to contain multiple
							signatures, the signing profile described in <xref linkend="signature" /> requires
							only a single <sgmltag class="starttag">Signature</sgmltag> element.  Use of multiple
							<sgmltag class="starttag">Signature</sgmltag> elements in an XRD document is therefore
							undefined.  In order to aid certain types of XRD consumers, it is
							<phrase role="keyword">recommended</phrase> that XRD providers place the
							<sgmltag class="starttag">Signature</sgmltag> element of a signed XRD as near the
							beginning of the document as possible.
						</para>
					</listitem>
				</varlistentry>

			</variablelist>
		</para>

		<para>
			The following schema fragment defines the <sgmltag class="starttag">XRD</sgmltag> element and its
			<sgmltag>XRDType</sgmltag> complex type:

			<programlisting><![CDATA[<element name="XRD" type="xrd:XRDType"/>
<complexType name="XRDType">
    <sequence>
        <element ref="xrd:Expires" minOccurs="0"/>
        <element ref="xrd:Subject" minOccurs="0"/>
        <choice minOccurs="0" maxOccurs="unbounded">
            <element ref="xrd:Alias"/>
            <element ref="xrd:Property"/>
            <element ref="xrd:Link"/>
            <any namespace="##other" processContents="lax"/>
        </choice>
    </sequence>
    <attribute ref="xml:id" use="optional"/>
    <anyAttribute namespace="##other" processContents="lax"/>
</complexType>]]></programlisting>
		</para>
	</section>

	<section id="element.expires">
		<title>Element <sgmltag class="starttag">Expires</sgmltag></title>
		<para>
			The <sgmltag class="starttag">Expires</sgmltag> element contains a time value which specifies the
			instant at and after which the document has expired and <phrase role="keyword">should not</phrase>
			be used.  The value <phrase role="keyword">must</phrase> be expressed in UTC form, as specified in
			<xref linkend="types.time" />, and <phrase role="keyword">must not</phrase> use fractional seconds.
		</para>

		<para>
			The semantics of this element apply to the metadata available in the XRD document and are independent
			of the caching semantics of any transport protocol used to retrieve the document.  If present, any
			cache expiration date specified by the transport protocol <phrase role="keyword">should not</phrase>
			be later than the time instant indicated by the <sgmltag class="starttag">Expires</sgmltag> element.
		</para>

		<para>
			The following schema fragment defines the <sgmltag class="starttag">Expires</sgmltag> element and its
			<sgmltag>ExpiresType</sgmltag> complex type:
			<programlisting><![CDATA[<element name="Expires" type="xrd:ExpiresType"/>
<complexType name="ExpiresType">
    <simpleContent>
        <extension base="dateTime">
            <anyAttribute namespace="##other" processContents="lax"/>
        </extension>
    </simpleContent>
</complexType>]]></programlisting>
		</para>
	</section>

	<section id="element.subject">
		<title>Element <sgmltag class="starttag">Subject</sgmltag></title>
		<para>
			The <sgmltag class="starttag">Subject</sgmltag> element contains a URI value which identifies
			the resource described by this XRD.  This value <phrase role="keyword">must</phrase> be an absolute URI.
			If <sgmltag class="starttag">Subject</sgmltag> is not specified, it is expected that the resource described
			by the XRD will be identified by other means.  Comparison of this value 
			<phrase role="keyword">must</phrase> be performed using the scheme-specific normalization rules for the 
			URI, as specified in Section 6.2.3 of <xref linkend="rfc3986" />.
		</para>

		<para>
			The following schema fragment defines the <sgmltag class="starttag">Subject</sgmltag> element:
			<programlisting><![CDATA[<element name="Subject" type="xrd:anyURI"/>]]></programlisting>
		</para>
	</section>

	<section id="element.alias">
		<title>Element <sgmltag class="starttag">Alias</sgmltag></title>
		<para>
			The <sgmltag class="starttag">Alias</sgmltag> element contains a URI value that is an additional
			identifier for the resource described by the XRD.  This value <phrase role="keyword">must</phrase> be
			an absolute URI.  The <sgmltag class="starttag">Alias</sgmltag> element does not identify additional
			resources the XRD is describing, but rather provides additional identifiers for the same resource.
			Comparison of this value <phrase role="keyword">must</phrase> be performed using the scheme-specific 
			normalization rules for the URI, as specified in Section 6.2.3 of <xref linkend="rfc3986" />.
		</para>

		<para>
			The following schema fragment defines the <sgmltag class="starttag">Alias</sgmltag> element:
			<programlisting><![CDATA[<element name="Alias" type="xrd:anyURI"/>]]></programlisting>
		</para>
	</section>

	<section id="element.property">
		<title>Element <sgmltag class="starttag">Property</sgmltag></title>
		<para>
			The <sgmltag class="starttag">Property</sgmltag> element declares a property of a resource (when used as a
			child of the <link linkend="element.xrd"><sgmltag class="starttag">XRD</sgmltag></link> element) or link
			relation (when used as a child of the
			<link linkend="element.link"><sgmltag class="starttag">Link</sgmltag></link> element), expressed as a
			key-value pair.  The key is identified by the <sgmltag class="attribute">type</sgmltag> attribute, and the
			value expressed as the string content of the <sgmltag class="starttag">Property</sgmltag> element.  A
			property <phrase role="keyword">may</phrase> have no value if the type identifier alone is sufficient.
			<sgmltag class="starttag">Property</sgmltag> elements that contain no value
			<phrase role="keyword">must</phrase> include the <sgmltag class="attribute">xsi:nil</sgmltag>
			attribute with a value of <sgmltag class="attvalue">true</sgmltag> as defined in
			<xref linkend="xml-schema" />.  <sgmltag class="starttag">Property</sgmltag> has the following
			attributes:

			<variablelist>
				<varlistentry>
					<term><sgmltag class="attribute">type</sgmltag> [Required]</term>
					<listitem>
						<para>
							The <sgmltag class="attribute">type</sgmltag> attribute is a URI that identifies the
							property being declared.  This value <phrase role="keyword">must</phrase> be an absolute
							URI.  This URI value is application-specific, and is used by the XRD provider to declare a
							property to consumers familiar with the type identifier.  Comparison of this value
							<phrase role="keyword">must</phrase> follow the same comparison rules used for comparing
							Link Relation Types as defined in <xref linkend="web-linking" />.
						</para>
					</listitem>
				</varlistentry>

			</variablelist>
		</para>
		<para>
			The following schema fragment defines the <sgmltag class="starttag">Property</sgmltag> element and its
			<sgmltag>PropertyType</sgmltag> complex type:
			<programlisting><![CDATA[<element name="Property" type="xrd:PropertyType" nillable="true"/>
<complexType name="PropertyType">
    <simpleContent>
        <extension base="xrd:string">
            <attribute name="type" type="anyURI" use="required"/>
        </extension>
    </simpleContent>
</complexType>]]></programlisting>
		</para>
	</section>

	<section id="element.link">
		<title>Element <sgmltag class="starttag">Link</sgmltag></title>
		<para>
			The <sgmltag class="starttag">Link</sgmltag> element serves as a container for metadata about a
			relation between the resource described by the XRD and a related resource.
		</para>

		<para>
			The semantics of this element are similar to the <xref linkend="html-4" /> Link element, the
			<xref linkend="atom" /> Link element, and the <link linkend="web-linking">HTTP Link Header</link>.
			The one distinction is that the link relation described by the <sgmltag class="starttag">Link</sgmltag>
			element is between the resource described by the XRD (referred to as the
			<glossterm>context</glossterm> resource by <xref linkend="web-linking" />) and the linked resource
			(referred to as the <glossterm>target</glossterm> resource by <xref linkend="web-linking" />), and not
			between the XRD document itself and the linked resource.
		</para>

		<para>
			The <sgmltag class="starttag">Link</sgmltag> element contains the following attributes and elements:

			<variablelist>

				<varlistentry id="link.attribute.rel">
					<term><sgmltag class="attribute">rel</sgmltag> [Optional]</term>
					<listitem>
						<para>
							This URI value defines the semantics of the relation between the resource described by
							the XRD and the linked resource.  This value <phrase role="keyword">must</phrase> be an
							absolute URI or a registered relation type, as defined in <xref linkend="web-linking" />.
							Comparison of this value <phrase role="keyword">must</phrase> follow the comparison rules
							for Link Relation Types defined in <xref linkend="web-linking" />.
						</para>

						<para>
							With one exception, the <sgmltag class="attribute">rel</sgmltag> attribute is semantically
							and syntactically equivalent to the Link Relation Types defined in
							<xref linkend="web-linking" />. It differs in that it only allows for a single relation
							type and does not allow for multiple space delimited values.
						</para>
						<para>
							It is important to note that this value does not identify any property of the linked
							resource.  Rather, it describes only how the linked resource is related to the resource
							described by the XRD.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry id="link.attribute.type">
					<term><sgmltag class="attribute">type</sgmltag> [Optional]</term>
					<listitem>
						<para>
							This string value identifies the media type of the linked resource, and
							<phrase role="keyword">must</phrase> be of the form of a media type as defined in
							<xref linkend="rfc4288" />.  The IANA media types registry can be found at
							<ulink url="http://www.iana.org/assignments/media-types/" />.  Comparison of this value
							<phrase role="keyword">must</phrase> be done in accordance with <xref linkend="rfc4288" />.
						</para>

						<para>
							Note that this is only a hint and does not override the media type declared by the
							linked resource itself (e.g. the Content-Type header of a HTTP response obtained by
							following the link).
						</para>
					</listitem>
				</varlistentry>

				<varlistentry id="link.attribute.href">
					<term><sgmltag class="attribute">href</sgmltag> [Optional]</term>
					<listitem>
						<para>
							The <sgmltag class="attribute">href</sgmltag> attribute provides the URI of the linked
							resource. If no <sgmltag class="attribute">href</sgmltag> attribute is defined, it is
							assumed the URI can be obtained from a <sgmltag class="attribute">template</sgmltag>
							attribute or by application-specific means.
						</para>
						<para>
							A <sgmltag class="starttag">Link</sgmltag> element <phrase role="keyword">may</phrase>
							contain an <sgmltag class="attribute">href</sgmltag> attribute or a
							<sgmltag class="attribute">template</sgmltag> attribute, but
							<phrase role="keyword">must not</phrase> contain both.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry id="link.attribute.template">
					<term><sgmltag class="attribute">template</sgmltag> [Optional]</term>
					<listitem>
						<para>
							The <sgmltag class="attribute">template</sgmltag> attribute provides a URI template
							which can be used to obtain the URI of the linked resource.	 Templates provide a
							mechanism for URI construction, taking a list of variables as input, and producing a
							URI string as an output.  The template syntax and vocabulary are determined by the
							application through which the XRD document is obtained and processed, and
							<phrase role="keyword">may</phrase> be specific to the link relation type indicated by
							the <sgmltag class="attribute">rel</sgmltag> attribute of the corresponding
							<sgmltag class="starttag">Link</sgmltag> element.  Applications utilizing the template
							mechanism <phrase role="keyword">must</phrase> define the template syntax and processing
							rules (including error handling) as well as the variable vocabulary.
						</para>
						<para>
							A <sgmltag class="starttag">Link</sgmltag> element <phrase role="keyword">may</phrase>
							contain an <sgmltag class="attribute">href</sgmltag> attribute or a
							<sgmltag class="attribute">template</sgmltag> attribute, but
							<phrase role="keyword">must not</phrase> contain both.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry>
					<term><sgmltag class="starttag">Title</sgmltag> [Zero or More]</term>
					<listitem>
						<para>
							Provides a human-readable description of the linked resource.  See
							<xref linkend="element.title" />.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry>
					<term><sgmltag class="starttag">Property</sgmltag> [Zero or More]</term>
					<listitem>
						<para>
							Declares a property of this link relation, as described in
							<xref linkend="element.property" />.  It is important to note that this value does not
							identify any property of the linked resource or the resource described by the XRD, but
							rather of the link relation between the linked resources.
						</para>
					</listitem>
				</varlistentry>

			</variablelist>
		</para>

		<para>
			The following schema fragment defines the <sgmltag class="starttag">Link</sgmltag> element and its
			<sgmltag>LinkType</sgmltag> complex type:
			<programlisting><![CDATA[<element name="Link" type="xrd:LinkType"/>
<complexType name="LinkType">
    <choice minOccurs="0" maxOccurs="unbounded">
        <element ref="xrd:Title"/>
        <element ref="xrd:Property"/>
        <any namespace="##other" processContents="lax"/>
    </choice>
    <attribute name="rel" type="anyURI" use="optional"/>
    <attribute name="type" type="string" use="optional"/>
    <attribute name="href" type="anyURI" use="optional"/>
    <attribute name="template" type="string" use="optional"/>
    <anyAttribute namespace="##other" processContents="lax"/>
</complexType>]]></programlisting>
		</para>
	</section>

	<section id="element.title">
		<title>Element <sgmltag class="starttag">Title</sgmltag></title>
		<para>
			The <sgmltag class="starttag">Title</sgmltag> element contains a string value that provides a
			human-readable description for the link.  This value is intended only for human consumption and
			<phrase role="keyword">must not</phrase> be used by an XRD consumer to affect the processing of the
			document. <sgmltag class="starttag">Title</sgmltag> contains the following attributes:

			<variablelist>
				<varlistentry>
					<term><sgmltag class="attribute">xml:lang</sgmltag> [Optional]</term>
					<listitem>
						<para>
							This attribute is defined by the <xref linkend="xml" /> specification, and is used to
							identify the natural language in which this element's content is written.
						</para>
					</listitem>
				</varlistentry>
			</variablelist>
		</para>
		<para>
			The following schema fragment defines the <sgmltag class="starttag">Title</sgmltag> element and its
			<sgmltag>TitleType</sgmltag> complex type:
			<programlisting><![CDATA[<element name="Title" type="xrd:TitleType"/>
<complexType name="TitleType">
    <simpleContent>
        <extension base="xrd:string">
            <attribute ref="xml:lang" use="optional"/>
        </extension>
    </simpleContent>
</complexType>
]]></programlisting>
		</para>
	</section>

</section>

<section id="extensibility">
	<title>XRD Extensibility</title>

	<para>
		The XRD schema defines only the elements necessary to support the most common use cases, with the
		explicit intention that applications will extend XRD to include other metadata about the resources
		they describe.  XRD documents can be extended by providing custom, meaningful values for certain URI-based
		attributes and elements, as well as by extending the XML schema directly.
	</para>

	<section id="identifier.extension">
		<title>Identifier Extension</title>

		<para>
			XRD uses URI-based identifiers for <link linkend="element.property">describing resources</link> as well
			as for <link linkend="link.attribute.rel">describing the relations</link> between resources. Whenever
			possible, applications <phrase role="keyword">should</phrase> use well-established URI identifiers for
			these purposes to promote interoperability and shared semantics.  Only when absolutely necessary should
			new URI identifiers be defined.  It is <phrase role="keyword">recommended</phrase> that any new identifiers
			be defined in a formal specification of use. The meaning of a given URI used as such an identifier
			<phrase role="keyword">should not</phrase> significantly change over time, and the identifier
			<phrase role="keyword">should not</phrase> be used to mean two different things.
		</para>

	</section>

	<section id="schema.extension">
		<title>Schema Extension</title>

		<para>
			The XRD schema allows for the inclusion of attributes from arbitrary namespaces (except for the XRD
			namespace) in almost all XRD elements.  Additionally, the <sgmltag class="starttag">XRD</sgmltag>
			and <sgmltag class="starttag">Link</sgmltag> elements allow for the inclusion of child elements from
			arbitrary namespaces (except for the XRD namespace).
		</para>

		<para>
			XML extensions <phrase role="keyword">must not</phrase> require new interpretation of elements defined
			in this document. If an extension attribute or element is present, an XRD consumer
			<phrase role="keyword">must</phrase> be able to ignore it and still correctly process the XRD document.
		</para>

		<para>
			This specification does not define generic rules for the comparison of string or URI values.  Therefore,
			specifications that include XRD schema extensions <phrase role="keyword">must</phrase> specify such
			comparison rules where necessary.
		</para>

	</section>

</section>

<section id="resource.selection">
	<title>Selecting Linked Resources</title>

	<para>
		Link selection criteria is determined by the XRD consumer's needs, and <phrase role="keyword">should</phrase>
		be based on the presence, absence, or value of the <sgmltag class="starttag">Link</sgmltag> element attributes
		or child elements.  The selection criteria is usually based on the value of the
		<sgmltag class="attribute">rel</sgmltag> attribute with the value of the
		<sgmltag class="attribute">type</sgmltag> attribute used as a hint (helping to determine if the linked
		resource uses a familiar media type).
	</para>

	<para>
		Selection based on multiple criteria <phrase role="keyword">should</phrase> be handled by performing multiple
		selections. Each selection is assigned preference order based on the consumer's needs, and the selection
		results are compared to determine the most desired set.  For example, an XRD consumer processing an XRD
		document describing an article may wish to select linked resources about the article's author.  If that
		consumer prefers HTML documents over plain text, then the linked resource selection would occur in two steps.
		First, all links with the <sgmltag class="attvalue">author</sgmltag> relation type would be selected, and if
		more than one are found, then the most appropriate link would be selected based on its media type.
	</para>

	<para>
		If multiple <sgmltag class="starttag">Link</sgmltag> elements are matched by a given selection criteria, they
		<phrase role="keyword">must</phrase> be processed in the order in which they appear in the XRD document.
		Therefore, XRD providers <phrase role="keyword">may</phrase> indicate element priority by placing them in a
		specific order.  If the first <sgmltag class="starttag">Link</sgmltag> is subsequently disqualified from the
		set of selected elements, the consumer <phrase role="keyword">should</phrase> attempt to select the next
		matching element in document order.  This process <phrase role="keyword">should</phrase> be continued for all
		other matching <sgmltag class="starttag">Link</sgmltag> elements until success is achieved or all elements are
		exhausted.
	</para>
</section>

<section id="signature">
	<title>XRD Signature</title>

	<para>
		An XRD provider <phrase role="keyword">may</phrase> digitally sign an XRD document in order to enable XRD
		consumers to verify the authenticity and integrity of the document.  The <xref linkend="xml-sig" />
		specification defines a general XML syntax for signing data that includes many options for flexibility. This
		section details constraints on these options so that XRD consumers do not have to implement the full generality
		of XML Signature processing.
	</para>

	<section id="signature.formats">
		<title>Signing Formats and Algorithms</title>

		<para>
			XRD documents <phrase role="keyword">must</phrase> use enveloped signatures as defined by
			<xref linkend="xml-sig" /> when signing.  Any signature algorithm defined by <xref linkend="xml-sig" />
			<phrase role="keyword">may</phrase> be used.
		</para>

	</section>

	<section id="signature.references">
		<title>References</title>

		<para>
			XRD documents <phrase role="keyword">must</phrase> supply a value for the
			<sgmltag class="attribute">xml:id</sgmltag> attribute on the root element of the XRD being signed. The
			XRD's root element may or may not be the root element of the actual XML document containing the signed XRD
			(e.g., it might be included within another document).
		</para>

		<para>
			Signatures <phrase role="keyword">must</phrase> contain a single
			<sgmltag class="starttag">ds:Reference</sgmltag> containing a same-document reference to the
			<sgmltag class="attribute">xml:id</sgmltag> attribute value of the root element of the XRD being signed.
			For example, if the <sgmltag class="attribute">xml:id</sgmltag> attribute value is
			<sgmltag class="attvalue">foo</sgmltag>, then the <sgmltag class="attribute">URI</sgmltag> attribute in
			the <sgmltag class="starttag">ds:Reference</sgmltag> element <phrase role="keyword">must</phrase> be
			<sgmltag class="attvalue">#foo</sgmltag>.
		</para>
	</section>

	<section id="signature.canonicalization">
		<title>Canonicalization</title>

		<para>
			XRD implementations <phrase role="keyword">must</phrase> use <xref linkend="excl-c14n" /> without comments,
			both in the <sgmltag class="starttag">ds:CanonicalizationMethod</sgmltag> element of
			<sgmltag class="starttag">ds:SignedInfo</sgmltag>, and as a
			<sgmltag class="starttag">ds:Transform</sgmltag> algorithm.
		</para>

		<para>
			Use of Exclusive Canonicalization facilitates the verification of signatures created over XRD instances
			when placed into a different XML context than present during signing.  Note that use of this algorithm
			alone does not guarantee that a particular signed object can be moved from one context to another safely,
			nor is that a requirement of signed XRD instances in general, though it may be required by particular
			profiles.
		</para>
	</section>

	<section id="signature.transforms">
		<title>Transforms</title>

		<para>
			Signatures in XRD documents <phrase role="keyword">must not</phrase> contain transforms other than the
			enveloped signature transform (with the identifier
			<literal>http://www.w3.org/2000/09/xmldsig#enveloped-signature</literal>) or the exclusive canonicalization
			transform (with the identifier <literal>http://www.w3.org/2001/10/xml-exc-c14n#</literal>).
		</para>
	</section>

	<section id="signature.keyinfo">
		<title>KeyInfo</title>

		<para>
			XML Signature defines usage of the <sgmltag class="starttag">ds:KeyInfo</sgmltag> element. XRD does not
			require the use of <sgmltag class="starttag">ds:KeyInfo</sgmltag>, nor does it impose any restrictions on
			its use. Therefore, <sgmltag class="starttag">ds:KeyInfo</sgmltag> <phrase role="keyword">may</phrase> be
			absent.
		</para>
	</section>

</section>

<section id="xrd.sequence">
	<title>XRD Sequence</title>

	<para>
		In cases where an application requires a sequence of <sgmltag class="starttag">XRD</sgmltag> elements in a
		single XML document, this specification defines an alternate top-level element,
		<sgmltag class="starttag">XRDS</sgmltag>.  This element <phrase role="keyword">should</phrase> contain either
		zero or more than one <sgmltag class="starttag">XRD</sgmltag> elements.  It has the following attributes and
		elements, and is not otherwise extensible:

			<variablelist>

				<varlistentry>
					<term><sgmltag class="attribute">ref</sgmltag> [Optional]</term>
					<listitem>
						<para>
							This URI value identifies the resource described by the sequence of
							<sgmltag class="starttag">XRD</sgmltag> elements.
						</para>
					</listitem>
				</varlistentry>

				<varlistentry>
					<term><sgmltag class="starttag">XRD</sgmltag> [Zero or More]</term>
					<listitem>
						<para>
							See <xref linkend="element.xrd" />.
						</para>
					</listitem>
				</varlistentry>

			</variablelist>
	</para>

	<para>
		The following schema fragment defines the <sgmltag class="starttag">XRDS</sgmltag> element and its
		<sgmltag>XRDSType</sgmltag> complex type:

		<programlisting><![CDATA[<element name="XRDS" type="xrd:XRDSType"/>
<complexType name="XRDSType">
    <sequence>
        <element ref="xrd:XRD" minOccurs="0" maxOccurs="unbounded"/>
    </sequence>
    <attribute name="ref" type="anyURI" use="optional"/>
</complexType>]]></programlisting>
	</para>
</section>

<section id="conformance">
	<title>Conformance</title>
	<para>
		An implementation is a <glossterm>conforming</glossterm> XRD Consumer if it meets the conditions in
		<xref linkend="conformance.consumer" />.  An implementation is a <glossterm>conforming</glossterm>
		Signature-Capable XRD Consumer if it meets the conditions in <xref linkend="conformance.sigconsumer" />.  An
		implementation is a <glossterm>conforming</glossterm> XRD Provider if it meets the conditions in
		<xref linkend="conformance.provider" />.  An implementation is a <glossterm>conforming</glossterm>
		Signature-Capable XRD Provider if it meets the conditions in <xref linkend="conformance.sigprovider" />.
		An implementation may serve as both an XRD consumer and provider.
	</para>

	<section id="conformance.consumer">
		<title>XRD Consumer</title>
		<para>
			An implementation conforms to this specification as an XRD Consumer if it meets the following conditions:

			<orderedlist spacing="compact">
				<listitem>
					<para>
						It <phrase role="keyword">must</phrase> implement parsing of XRD documents as defined in
						<xref linkend="document.structure" />. Support for XRDS documents, as defined in
						<xref linkend="xrd.sequence" />, is <phrase role="keyword">optional</phrase>.
					</para>
				</listitem>
				<listitem>
					<para>
						It <phrase role="keyword">must</phrase> conform to the processing rules as specified in
						<xref linkend="resource.selection" />.
					</para>
				</listitem>
			</orderedlist>
		</para>
	</section>

	<section id="conformance.sigconsumer">
		<title>Signature-Capable XRD Consumer</title>
		<para>
			An implementation conforms to this specification as a Signature-Capable XRD Consumer if it meets the
			following conditions:

			<orderedlist spacing="compact">
				<listitem>
					<para>
						It <phrase role="keyword">must</phrase> meet all conformance requirements of an XRD Consumer
						as defined by <xref linkend="conformance.consumer" />.
					</para>
				</listitem>
				<listitem>
					<para>
						It <phrase role="keyword">must</phrase> support the verification of signed XRD documents as
						defined by <xref linkend="signature" />, and <phrase role="keyword">must</phrase> support the
						digital signature algorithm identified by
						<literal>http://www.w3.org/2000/09/xmldsig#rsa-sha256</literal>, as defined by
						<xref linkend="xml-sig" />.
					</para>
				</listitem>
			</orderedlist>
		</para>
	</section>

	<section id="conformance.provider">
		<title>XRD Provider</title>
		<para>
			An implementation conforms to this specification as an XRD Provider if it meets the following
			conditions:

			<orderedlist spacing="compact">
				<listitem>
					<para>
						It <phrase role="keyword">must</phrase> support the creation of XRD documents as defined in
						<xref linkend="document.structure" />. Support for XRDS documents, as defined in
						<xref linkend="xrd.sequence" />, is <phrase role="keyword">optional</phrase>.
					</para>
				</listitem>
			</orderedlist>
		</para>
	</section>

	<section id="conformance.sigprovider">
		<title>Signature-Capable XRD Provider</title>
		<para>
			An implementation conforms to this specification as a Signature-Capable XRD Provider if it meets the
			following conditions:

			<orderedlist spacing="compact">
				<listitem>
					<para>
						It <phrase role="keyword">must</phrase> meet all conformance requirements of an XRD Provider
						as defined by <xref linkend="conformance.provider" />.
					</para>
				</listitem>
				<listitem>
					<para>
						It <phrase role="keyword">must</phrase> support the creation of signed XRD documents as
						defined by <xref linkend="signature" />, and <phrase role="keyword">must</phrase> support the
						digital signature algorithm identified by
						<literal>http://www.w3.org/2000/09/xmldsig#rsa-sha256</literal>, as defined by
						<xref linkend="xml-sig" />.
					</para>
				</listitem>
			</orderedlist>
		</para>
	</section>
</section>

<appendix id="acknowledgements" role="non-normative">
	<title>Acknowledgments</title>

	<para>
		The editors would like to thank the following current and former members of the OASIS XRI TC
		for their particular contributions to this and previous versions of this specification:
	</para>

	<itemizedlist spacing="compact">
		<listitem><para>Dirk Balfanz, Google</para></listitem>
		<listitem><para>Bill Barnhill, Booz Allen Hamilton</para></listitem>
		<listitem><para>John Bradley</para></listitem>
		<listitem><para>Scott Cantor, Internet2</para></listitem>
		<listitem><para>Les Chasen, NeuStar</para></listitem>
		<listitem><para>Steven Churchill, XDI.org</para></listitem>
		<listitem><para>Brian Eaton, Google</para></listitem>
		<listitem><para>George Fletcher, AOL</para></listitem>
		<listitem><para>Victor Grey, Planetwork</para></listitem>
		<listitem><para>Joseph Holsten</para></listitem>
		<listitem><para>Nika Jones</para></listitem>
		<listitem><para>Breno de Medeiros, Google</para></listitem>
		<listitem><para>Bob Morgan, Internet2</para></listitem>
		<listitem><para>Markus Sabadello, XDI.org</para></listitem>
		<listitem><para>Nat Sakimura, NRI</para></listitem>
		<listitem><para>Tatsuki Sakushima, NRI</para></listitem>
		<listitem><para>William Tan, NeuStar</para></listitem>
		<listitem><para>Gabe Wachob</para></listitem>
	</itemizedlist>

	<para>
		The editors would also like to acknowledge the contributions of the other members of the OASIS
		XRI Technical Committee, whose other voting members at the time of publication were:
	</para>

	<itemizedlist spacing="compact">
		<listitem><para>Giovanni Bartolomeo, University of Rome "Tor Vergata"</para></listitem>
		<listitem><para>Owen Davis, Planetwork</para></listitem>
		<listitem><para>Jeff Hodges</para></listitem>
		<listitem><para>Fen Labalme, Planetwork</para></listitem>
		<listitem><para>Ben Laurie, Google</para></listitem>
		<listitem><para>XiaoDong Lee, China Internet Network Information Center</para></listitem>
		<listitem><para>Nick Nicholas, Australian Department of Education</para></listitem>
		<listitem><para>Marty Schleiff, The Boeing Company</para></listitem>
		<listitem><para>Paul Trevithick</para></listitem>
	</itemizedlist>

</appendix>

<!-- To ensure the PDF version of the spec is displayed properly, examples should not exceed 78 columns in width -->
<appendix id="examples" role="non-normative">
	<title>XRD Examples</title>

	<example id="examples.1">
		<title>Simple XRD Example</title>
		<programlisting><![CDATA[<XRD xmlns="http://docs.oasis-open.org/ns/xri/xrd-1.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Expires>1970-01-01T00:00:00Z</Expires>
  <Subject>http://example.com/gpburdell</Subject>
  <Property type="http://spec.example.net/type/person" xsi:nil="true" />
  <Link rel="http://spec.example.net/auth/1.0"
    href="http://services.example.com/auth" />
  <Link rel="http://spec.example.net/photo/1.0" type="image/jpeg"
    href="http://photos.example.com/gpburdell.jpg">
    <Title xml:lang="en">User Photo</Title>
    <Title xml:lang="de">Benutzerfoto</Title>
    <Property type="http://spec.example.net/created/1.0">1970-01-01</Property>
  </Link>
</XRD>
]]></programlisting>
	</example>

	<example id="examples.2">
		<?dbfo keep-together="auto"?>
		<title>Signed XRD Example</title>

		<para>
			Following is an example of a signed XRD document.  Line breaks have been added for readability; the
			signatures are not valid and cannot be successfully verified.
		</para>

		<programlisting><![CDATA[<XRD xmlns="http://docs.oasis-open.org/ns/xri/xrd-1.0" xml:id="foo">
  <Expires>1970-01-01T00:00:00Z</Expires>
  <Subject>http://example.com/gpburdell</Subject>
  <Alias>http://people.example.com/gpburdell</Alias>
  <Alias>acct:gpburdell@example.com</Alias>
  <Property type="http://spec.example.net/version">1.0</Property>
  <Property type="http://spec.example.net/version">2.0</Property>
  <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
    <ds:SignedInfo>
      <ds:CanonicalizationMethod
        Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
      <ds:SignatureMethod
        Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/>
      <ds:Reference URI="#foo">
        <ds:Transforms>
          <ds:Transform
           Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
          <ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#">
            <InclusiveNamespaces PrefixList="#default xrd ds xs xsi"
              xmlns="http://www.w3.org/2001/10/xml-exc-c14n#"/>
          </ds:Transform>
        </ds:Transforms>
        <ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
        <ds:DigestValue>TCDVSuG6grhyHbzhQFWFzGrxIPE=</ds:DigestValue>
      </ds:Reference>
    </ds:SignedInfo>
    <ds:SignatureValue>
      x/GyPbzmFEe85pGD3c1aXG4Vspb9V9jGCjwcRCKrtwPS6vdVNCcY5rHaFPYWkf+5
      EIYcPzx+pX1h43SmwviCqXRjRtMANWbHLhWAptaK1ywS7gFgsD01qjyen3CP+m3D
      w6vKhaqledl0BYyrIzb4KkHO4ahNyBVXbJwqv5pUaE4=
    </ds:SignatureValue>
    <ds:KeyInfo>
      <ds:X509Data>
        <ds:X509Certificate>
          MIICyjCCAjOgAwIBAgICAnUwDQYJKoZIhvcNAQEEBQAwgakxCzAJBgNVBAYTAlVT
          MRIwEAYDVQQIEwlXaXNjb25zaW4xEDAOBgNVBAcTB01hZGlzb24xIDAeBgNVBAoT
          F1VuaXZlcnNpdHkgb2YgV2lzY29uc2luMSswKQYDVQQLEyJEaXZpc2lvbiBvZiBJ
          bmZvcm1hdGlvbiBUZWNobm9sb2d5MSUwIwYDVQQDExxIRVBLSSBTZXJ2ZXIgQ0Eg
          LS0gMjAwMjA3MDFBMB4XDTAyMDcyNjA3Mjc1MVoXDTA2MDkwNDA3Mjc1MVowgYsx
          CzAJBgNVBAYTAlVTMREwDwYDVQQIEwhNaWNoaWdhbjESMBAGA1UEBxMJQW5uIEFy
          Ym9yMQ4wDAYDVQQKEwVVQ0FJRDEcMBoGA1UEAxMTc2hpYjEuaW50ZXJuZXQyLmVk
          dTEnMCUGCSqGSIb3DQEJARYYcm9vdEBzaGliMS5pbnRlcm5ldDIuZWR1MIGfMA0G
          CSqGSIb3DQEBAQUAA4GNADCBiQKBgQDZSAb2sxvhAXnXVIVTx8vuRay+x50z7GJj
          IHRYQgIv6IqaGG04eTcyVMhoekE0b45QgvBIaOAPSZBl13R6+KYiE7x4XAWIrCP+
          c2MZVeXeTgV3Yz+USLg2Y1on+Jh4HxwkPFmZBctyXiUr6DxF8rvoP9W7O27rhRjE
          pmqOIfGTWQIDAQABox0wGzAMBgNVHRMBAf8EAjAAMAsGA1UdDwQEAwIFoDANBgkq
          hkiG9w0BAQQFAAOBgQBfDqEW+OI3jqBQHIBzhujN/PizdN7s/z4D5d3pptWDJf2n
          qgi7lFV6MDkhmTvTqBtjmNk3No7v/dnP6Hr7wHxvCCRwubnmIfZ6QZAv2FU78pLX
          8I3bsbmRAUg4UP9hH6ABVq4KQKMknxu1xQxLhpR1ylGPdiowMNTrEG8cCx3w/w==
        </ds:X509Certificate>
      </ds:X509Data>
    </ds:KeyInfo>
  </ds:Signature>
  <Link rel="http://spec.example.net/auth/1.0"
    href="http://services.example.com/auth" />
</XRD>
]]></programlisting>
	</example>

</appendix>

<appendix id="media-type" role="non-normative">
	<title>Media Type Definition for <literal>application/xrd+xml</literal></title>

	<para>
		This section is prepared in anticipation of filing a media type registration meeting the requirements of
		<xref linkend="rfc4288" />.
	</para>

	<variablelist>
		<varlistentry>
			<term>Type name:</term>
			<listitem>
				<para><code>application</code></para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Subtype name:</term>
			<listitem>
				<para><code>xrd+xml</code></para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Required parameters:</term>
			<listitem>
				<para>None</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Optional parameters:</term>
			<listitem>
				<para>
					"charset":  This parameter has identical semantics to the charset
					parameter of the "application/xml" media type as specified in <xref linkend="rfc3023" />.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Encoding considerations:</term>
			<listitem>
				<para>
					Identical to those of <code>application/xml</code> as described by <xref linkend="rfc3023" />
					section 3.2.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Security considerations:</term>
			<listitem>
				<para>
					As defined in this specification. In addition, as this media type uses the
					"+xml" convention, it shares the same security considerations as described in
					<xref linkend="rfc3023" />, Section 10.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Interoperability considerations:</term>
			<listitem>
				<para>There are no known interoperability issues.</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Published specification:</term>
			<listitem>
				<para>This specification</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Applications that use this media type:</term>
			<listitem>
				<para>No known applications currently use this media type.</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Magic Number:</term>
			<listitem>
				<para>As specified for <xref linkend="rfc3023" /> section 3.2.</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>File Extension:</term>
			<listitem>
				<para>
					None.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Fragment Identifiers:</term>
			<listitem>
				<para>
					As specified for <xref linkend="rfc3023" /> section 5.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Base URI:</term>
			<listitem>
				<para>
					As specified for <xref linkend="rfc3023" /> section 6.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Macintosh File Type code:</term>
			<listitem>
				<para>
					TEXT.
				</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Person &amp; email address to contact for further information:</term>
			<listitem>
				<para>Eran Hammer-Lahav, eran@hueniverse.com</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Intended usage:</term>
			<listitem>
				<para>COMMON</para>
			</listitem>
		</varlistentry>

		<varlistentry>
			<term>Author / Change controller:</term>
			<listitem>
				<para>OASIS XRI Technical Committee</para>
			</listitem>
		</varlistentry>

	</variablelist>

</appendix>

<appendix id="revisions" role="non-normative">
	<title>Revision History</title>

	<table>
		<?dbfo keep-together="auto"?>
		<tgroup cols="4">
			<thead>
				<row>
					<entry>Revision</entry>
					<entry>Date</entry>
					<entry>Editor</entry>
					<entry>Changes Made</entry>
				</row>
			</thead>
			<tbody>
				<row>
					<entry>Committee Draft 02</entry>
					<entry>9 March 2010</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>Approved by the XRI Technical Committee as Committee Draft 02.</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 15</entry>
					<entry>24 February 2010</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>Minor editorial changes with comparison language.</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 14</entry>
					<entry>18 February 2010</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>Reference rfc4288 instead of rfc2046 for definition of media types</para>
							</listitem>
							<listitem>
								<para>
									Add explicit comparison rules for Subject, Alias, Link type, and Property type.  
									XRD schema extensions MUST declare their own comparison rules where appropriate.
								</para>
							</listitem>
							<listitem>
								<para>Minor editorial changes.</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 13</entry>
					<entry>21 January 2010</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>Clarify different uses of Property element</para>
							</listitem>
							<listitem>
								<para>Regarding URI templates, Applications MUST define template syntax</para>
							</listitem>
							<listitem>
								<para>In Identifier Extension section, emphasize re-use of existing identifers</para>
							</listitem>
							<listitem>
								<para>In Identifier Extension section, make last sentence normative "SHOULD NOT"</para>
							</listitem>
							<listitem>
								<para>Move "Linked Resource Selection" section up one level</para>
							</listitem>
							<listitem>
								<para>Various minor editorial changes</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 12</entry>
					<entry>16 January 2010</entry>
					<entry>willnorris, cantor.2</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>Remove XRI 3.0 as a "related specification"</para>
							</listitem>
							<listitem>
								<para>Remove intro paragraph for common data types</para>
							</listitem>
							<listitem>
								<para>Combine element definitions into single section</para>
							</listitem>
							<listitem>
								<para>More consistent language for descripting elements</para>
							</listitem>
							<listitem>
								<para>
									Reword several descriptions to place additional emphasis on declaritive description
									before noting similarities, additional notes, etc.  (Link, Link/@rel, Link/@type,
									XRDS)
								</para>
							</listitem>
							<listitem>
								<para>
									Clarify semantics of Expires element as well as relationship with transport level
									expiration date
								</para>
							</listitem>
							<listitem>
								<para>
									URI for a Link with an href or template attribute is "application-specific"
								</para>
							</listitem>
							<listitem>
								<para>Clarify restrictions on use of Title element</para>
							</listitem>
							<listitem>
								<para>Make XRD processing text normative</para>
							</listitem>
							<listitem>
								<para>Cleanup language in XRD Signature sections</para>
							</listitem>
							<listitem>
								<para>
									Reworked conformance text and created separate conformance targets for signature
									handling
								</para>
							</listitem>
							<listitem>
								<para>Demonstrate multiple Titles and Link-level Property in example XRD</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 11</entry>
					<entry>17 December 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>
									Clarify that XRD Signatures must use Exclusive Canonicalization without comments.
								</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 10</entry>
					<entry>19 November 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>
									Replace Type element with Property, which allows for a key-value pair.  Add
									Property as a child element of Link
								</para>
							</listitem>
							<listitem>
								<para>
									Change Rel, MediaType, URI, and URITemplate elements to be attributes of Link named
									rel, type, href, and template respectively.
								</para>
							</listitem>
							<listitem>
								<para>Fix cardinality of XRD child elements of XRDS.</para>
							</listitem>
							<listitem>
								<para>
									Additional text to clarify intended use of Subject, Alias, and Property elements,
									as well as type attribute.
								</para>
							</listitem>
							<listitem>
								<para>Links MUST NOT contain both 'uri' and 'template' attributes.</para>
							</listitem>
							<listitem>
								<para>Focus link selection on 'rel', using 'type' only as a useful hint.</para>
							</listitem>
							<listitem>
								<para>
									Replace text about ignoring links with unknown template syntax with instructions to
									follow the protocol-specific rules on handling bad templates
								</para>
							</listitem>
							<listitem>
								<para>
									Update examples to reflect new schema and demonstrate use of a few more elements.
								</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Committee Draft 01</entry>
					<entry>22 October 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>Approved by the XRI Technical Committee as Committee Draft 01.</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 09</entry>
					<entry>15 October 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>
									Cleanup references section (some where no longer referenced at all, some were only
									informative).
								</para>
							</listitem>
							<listitem>
								<para>Fix acknowledgements to properly include XRI Resolution 2.0 editors</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 08</entry>
					<entry>14 October 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>
									Remove "Subject" "ds:keyInfo" as child elements of Link.  These only had clear
									meaning in the context of a linked XRD.
								</para>
							</listitem>
							<listitem>
								<para>
									Remove default URI template syntax and change text to make it application+relation
									specific
								</para>
							</listitem>
							<listitem>
								<para>
									Clarified that rel values are not allowed to contain space-delimited relation types
								</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 07</entry>
					<entry>12 October 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>
									Remove "Extensions" element. Revert to previous extension model, resolving the
									"ambiguous schema" issue by simply not defining the signature elements in the XRD
									schema.
								</para>
							</listitem>
							<listitem>
								<para>
									Add "Title" element under "Link" for human readable name of linked resource
								</para>
							</listitem>
							<listitem>
								<para>Add signature algorithm support to conformance</para>
							</listitem>
							<listitem>
								<para>
									Greatly reduce complexity of Link element.  Reduce cardinality of Rel, MediaType,
									URI, and URITemplate elements to zero or one.  URI or URITemplate is allowed, but
									not both.  Processing section updated to reflect these changes.
								</para>
							</listitem>
							<listitem>
								<para>Remove definition of linked XRD documents.</para>
							</listitem>
							<listitem>
								<para>Various minor editorial changes</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 06</entry>
					<entry>04 September 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>
									Combine "Document Property Elements" and "Resource Property Elements" into "XRD
									Elements"
								</para>
							</listitem>
							<listitem>
								<para>Move schema and references to first section</para>
							</listitem>
							<listitem>
								<para>Promote "XRD Extensions" section, and move schema fragment</para>
							</listitem>
							<listitem>
								<para>Add example for URI / URITemplate processing order</para>
							</listitem>
							<listitem>
								<para>Move XRD Example into an appendix</para>
							</listitem>
							<listitem>
								<para>Various minor rewording</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 05</entry>
					<entry>01 September 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>
									Remove priority attribute on Link, URI, and URITemplate elements.  Instead, element
									priority is implied by document order.  Additionally, requirement for consumers to
									respect priority strengthened from "should" to "must".
								</para>
							</listitem>
							<listitem>
								<para>
									New "Extensions" element added to XRD and Link elements as the sole location to
									extend XRD with arbitrary child elements.
								</para>
							</listitem>
							<listitem>
								<para>Define "XRDS" element to contain a sequence of XRD elements.</para>
							</listitem>
							<listitem>
								<para>Removed "match" attribute from Subject.</para>
							</listitem>
							<listitem>
								<para>
									Added requirement to follow normal rules for Rel values (either use a URI, or
									register value with IANA)
								</para>
							</listitem>
							<listitem>
								<para>
									Switched from Relax NG to XSD as the authoritative schema language for the XRD
									Schema.  (Primarily due to the lack of a Relax NG schema for XML DSig)
								</para>
							</listitem>
							<listitem>
								<para>Clarify language regarding URIs and URI Templates</para>
							</listitem>
							<listitem>
								<para>Define "Common Data Types" for XRD</para>
							</listitem>
							<listitem>
								<para>Various minor editorial and grammatical changes</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 04</entry>
					<entry>12 August 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>
									Remove XRD Trust section, pushing that work to separate trust profiles.  Move XRD
									Signature section up one level.
								</para>
							</listitem>
							<listitem>
								<para>Remove requirement for explicit Link Subject on linked XRDs</para>
							</listitem>
							<listitem>
								<para>Use non-information URI for rel value to designate linked XRD</para>
							</listitem>
							<listitem>
								<para>Flesh out subject matching rules</para>
							</listitem>
							<listitem>
								<para>Remove "must not be used" from Expires element description</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 03</entry>
					<entry>04 August 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>
									Revert to previous processing flow for related resources -- first filter, then sort
									by priority
								</para>
							</listitem>
							<listitem>
								<para>Add media type definition for "application/xrd+xml"</para>
							</listitem>
							<listitem>
								<para>Clarify text for URI templates</para>
							</listitem>
							<listitem>
								<para>Strengthen requirement to use excl-c14n from "should" to "must"</para>
							</listitem>
							<listitem>
								<para>Move Signature element to bottom of the document for readability</para>
							</listitem>
							<listitem>
								<para>Add conformance section</para>
							</listitem>
							<listitem>
								<para>
									Add "match" attribute to Subject element.  Also add stub section for subject
									matching.
								</para>
							</listitem>
							<listitem>
								<para>Add XSD schema (in addition to RELAX NG)</para>
							</listitem>
							<listitem>
								<para>Various editorial and grammatical changes.</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 02</entry>
					<entry>03 July 2009</entry>
					<entry>willnorris</entry>
					<entry>
						<itemizedlist spacing="compact">
							<listitem>
								<para>
									Remove XRD Trust namespace and elements (TargetSubject replaced by Subject,
									TargetAuthority replaced by ds:KeyInfo)
								</para>
							</listitem>
							<listitem>
								<para>
									Section added for XML Digital Signature, primarily copied from SAML 2.0, which
									changes as necessary
								</para>
							</listitem>
							<listitem>
								<para>
									Language clarified on priority attribute values ('null' is not a valid value)
								</para>
							</listitem>
							<listitem>
								<para>Add section for XRD Extensibility</para>
							</listitem>
							<listitem>
								<para>
									Only require XML element order for elements with cardinality of "zero or one"
								</para>
							</listitem>
							<listitem>
								<para>Add section for defining linked XRD documents</para>
							</listitem>
							<listitem>
								<para>
									Processing rules changed for related resources to first sort by priority, then
									filter.  Also add processing rule for linked XRD documents.
								</para>
							</listitem>
							<listitem>
								<para>Various editorial and grammatical changes.</para>
							</listitem>
						</itemizedlist>
					</entry>
				</row>

				<row>
					<entry>Working Draft 01</entry>
					<entry>09 May 2009</entry>
					<entry>willnorris</entry>
					<entry>Initial Publication</entry>
				</row>
			</tbody>
		</tgroup>
	</table>
</appendix>

</article>
