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xdi-core-1.0-wd06.xml
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<?xml version="1.0" encoding="UTF-8"?>
<!--
For use when a committee document points at the OASIS web site for publishing:
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href="http://docs.oasis-open.org/templates/DocBook/spec-0.6/stylesheets/oasis-specification-html.xsl"?>
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For use when a committee document points to an embedded runtime installation:
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For use when a committee document is published in a local environment only
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "../../htmlruntime/spec-0.6/docbook/docbookx.dtd"[
<!ENTITY title "XDI Core V&version;">
<!ENTITY name "xdi-core">
<!ENTITY pversion "0.1">
<!ENTITY version "1.0">
<!ENTITY pubdate "19 October 2015">
<!ENTITY stage "wd06">
<!ENTITY standard "Working Draft 06">
<!ENTITY this-loc "http://docs.oasis-open.org/xdi/spec-&version;">
<!ENTITY previous-loc "http://docs.oasis-open.org/xdi/spec-&pversion;">
<!ENTITY latest-loc "http://docs.oasis-open.org/xdi/spec">
]>
<!--DOCTYPE article PUBLIC "-//OASIS//DTD DocBook SVG Module V1.1CR1//EN" "http://www.oasis-open.org/docbook/xml/svg/1.1CR1/dbsvg.dtd"-->
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<!--article status="&standard;" xmlns="http://docbook.org/ns/docbook" version="5.0" xml:lang="en"-->
<article xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink"
version="4.4" xml:lang="en" status="&standard;">
<articleinfo>
<title>&title;</title>
<productname>&name;</productname>
<productnumber>&version;-&stage;</productnumber>
<releaseinfo role="track">Standards Track Work Product</releaseinfo>
<releaseinfo role="OASIS-specification-this-authoritative"
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>&previous-loc;/&name;-&pversion;.xml</releaseinfo>
<releaseinfo role="OASIS-specification-previous"
>&previous-loc;/&name;-&pversion;.pdf</releaseinfo>
<releaseinfo role="OASIS-specification-previous"
>&previous-loc;/&name;-&pversion;.html</releaseinfo>
<releaseinfo role="OASIS-specification-latest-authoritative"
>&latest-loc;/&name;.xml</releaseinfo>
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<releaseinfo role="OASIS-specification-latest">&latest-loc;/&name;.html</releaseinfo>
<releaseinfo role="committee"><ulink url="http://www.oasis-open.org/committees/xdi">OASIS
XDI TC</ulink></releaseinfo>
<authorgroup>
<editor>
<firstname>Joseph</firstname>
<surname>Boyle</surname>
<affiliation>
<orgname>XDI.org</orgname>
</affiliation>
<email>joseph@xdi.org</email>
</editor>
<editor>
<firstname>Drummond</firstname>
<surname>Reed</surname>
<affiliation>
<orgname>Respect Network</orgname>
</affiliation>
<email>drummond@respect.network</email>
</editor>
<editor>
<firstname>Markus</firstname>
<surname>Sabadello</surname>
<affiliation>
<orgname>XDI.org</orgname>
</affiliation>
<email>markus.sabadello@xdi.org</email>
</editor>
</authorgroup>
<pubdate>&pubdate;</pubdate>
<copyright>
<year>2015</year>
<holder>OASIS Open, Inc. All Rights Reserved.</holder>
</copyright>
<legalnotice role="additional">
<title>Additional artifacts</title>
<para>This prose specification is one component of a Work Product which also
includes:</para>
<!--itemizedlist spacing="compact"> <listitem><para><para>
publishing materials: <ulink url="&this-loc;/&name;-&version;-&stage;.zip">&this-loc;/&name;-&version;-&stage;.zip</ulink></para>
</para></listitem> </itemizedlist-->
</legalnotice>
<legalnotice role="related">
<title>Related work</title>
<para/>
</legalnotice>
<abstract>
<title>Abstract</title>
<para>This working draft is for reviewer comment only and is not yet a standards
document or published at OASIS. This is the core specification for XDI (Extensible
Data Interchange). It defines the XDI semantic graph model, ABNF, JSON
serialization, and addressing rules.</para>
</abstract>
<!--legalnotice role="status"><title>Status</title>
<para>This is a work in progress contributed to the OASIS TC administration
and does not at this time represent the consensus of any particular OASIS Technical Committee.
There are no plans to make this a formal Committee Specification as it is merely an internal
document made available to committee members to support the publishing process.</para>
</legalnotice-->
<legalnotice role="citation">
<title>Citation format</title>
<para>When referencing this specification the following citation format should be
used:</para>
<!--bibliolist> <bibliomixed>
<abbrev>OASIS-XDI-Core-V1.0</abbrev>
<title>OASIS XDI Core V1.0</title>
<date>&pubdate;. </date>
<releaseinfo>OASIS &standard;. </releaseinfo>
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<legalnotice role="notices">
<title>Notices</title>
<para>Copyright © OASIS® Open 2015. All Rights Reserved. </para>
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>http://www.oasis-open.org/who/intellectualproperty.php</ulink>.</para>
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</articleinfo>
<para><quote>I would not give a fig for the simplicity this side of complexity, but I would give
my life for the simplicity on the other side of complexity.</quote> —Oliver Wendell
Holmes, Jr.</para>
<para><quote>Everything should be made as simple as possible, but no simpler.</quote> —Albert
Einstein</para>
<para><quote>It's turtles all the way down!</quote> —Dr. Seuss</para>
<section id="introduction">
<title>Introduction</title>
<para>This is the core specification for XDI (Extensible Data Interchange). It defines the
XDI semantic graph model, ABNF, JSON serialization, and addressing rules.</para>
<section>
<title>How XDI Builds On RDF</title>
<para>RDF (Resource Description Framework) <xref linkend="rdf-concepts"/> is the W3C
standard for the foundation of the Semantic Web. It defines a core semantic graph
model based on subject-predicate-object triples for describing data. The W3C has
also defined JSON-LD <xref linkend="json-ld"/> and the W3C Linked Data Platform 1.0
<xref linkend="ldplatform"/> as W3C Recommendations. </para>
<para>XDI builds on the RDF graph model, adding several key features and constraints in
order to optimize it for semantic data interchange. The most important of these
are:</para>
<orderedlist>
<listitem>
<para><emphasis role="bold">Context. </emphasis>XDI makes context another
dimension of the graph model—to the point where contextual statements are
the third fundamental type of XDI statement along with literal and
relational statements.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Addressability. </emphasis>The XDI graph model does
not allow RDF blank nodes. It also imposes the constraint that the XDI
identifier of every XDI contextual arc must be unique it the scope of its
parent node. The result is that every node of every XDI graph has a unique
global address—and the address itself is a semantic description of that
node.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Simplified reification. </emphasis>The XDI graph
model has a standard mechanism for reification of any XDI statement, and
reified statements are also uniquely addressable.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Immutability. </emphasis>Persistent identity is so
important in distributed data sharing that XDI addressing includes special
syntax for immutable identifiers of XDI graph nodes.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Relativity. </emphasis>Identifier scope is also
critical to interoperable semantics, so XDI addressing supports explicit
syntax for both absolute and relative identifiers of XDI graph nodes.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Authority. </emphasis>Establishing a clear chain of
authority and accountability for shared data is also a key requirement of
semantic data interchange. XDI contexts and classes enable directly modeling
of real-world legal relationships and responsibilities.</para>
</listitem>
</orderedlist>
<para>The result is an addressable semantic tree model that brings together the benefits
of Semantic Web technology with the benefits of well-established directory tree
technologies, as shown in the following diagram.</para>
<svg width="500" height="300" viewBox="0 0 500 150" version="1.1"
xmlns="http://www.w3.org/2000/svg">
<ellipse cx="250" cy="70" rx="248" ry="140" stroke="black" stroke-width="2" fill="white"/>
<g transform="translate(130,0)">
<circle cx="0" cy="70" r="105" stroke="black" fill="white"/>
<text x="0" y="0" text-anchor="middle">Semantic Web:</text>
<text x="0" y="40" text-anchor="middle">Description Logic</text>
<text x="0" y="60" text-anchor="middle">Knowledge Representation</text>
<text x="0" y="80" text-anchor="middle">Machine Learning</text>
<text x="0" y="120" text-anchor="middle">RDF, OWL, JSON-LD</text>
</g>
<g transform="translate(360,0)">
<circle cx="0" cy="70" r="105" stroke="black" fill="white"/>
<text x="0" y="0" text-anchor="middle">Directory Tree:</text>
<text x="0" y="40" text-anchor="middle">Identity Management</text>
<text x="0" y="60" text-anchor="middle">Discovery, Access Control</text>
<text x="0" y="80" text-anchor="middle">Authentication, Authorization</text>
<text x="0" y="120" text-anchor="middle">X.500, LDAP, DNS</text>
<text x="0" y="140" text-anchor="middle">XACML, OAuth</text>
</g>
<text x="250" y="-40" text-anchor="middle">Semantic Tree:</text>
<text x="250" y="180" text-anchor="middle">XDI</text>
</svg>
<para>Additional comparisons with specific features of the RDF family of specifications
will be covered throughout this specification.</para>
</section>
<section>
<title>Example XDI Graphs</title>
<para>This is an example XDI graph shown in XDI JSON serialization format. It is a
relatively simple graph showing some typical profile data for a person (Alice).
Alice’s graph also includes a reference to the peer graph for another person (Bob). </para>
<note>
<para>In the examples used in this specification: a) mutable XDI identifiers (XDI
names) will often use the "x-" prefix reserved for examples, and 2) immutable
XDI identifiers that use XDI UUID scheme will often use truncated placeholders
in the form of ":uuid:x-" for readability.</para>
</note>
<programlisting>{
"<$iri>": {
"&": "https://xdi.example.com/=!:uuid:x-alice/"
},
"=!:uuid:x-alice": {
"/#friend": [
"=!:uuid:x-bob"
],
"<#home><#email>": {
"&": "alice@example.com"
},
"<#work><#email>": {
"&": "asmith@example.net"
},
"<#personal><#email>": {
"/$ref": [
"=!:uuid:x-alice<#home><#email>"
]
}
},
"=!:uuid:x-alice#passport": {
"<#country>": {
"&": "Canada"
},
"<#name>": {
"&": "Alice Smith"
},
"<#num>": {
"&": "1234567"
}
},
"(=!:uuid:x-bob)": {
"<$iri>": {
"&": "https://xdi.example.com/=!:uuid:x-bob/"
}
}
}</programlisting>
<para>This second example adds some additional XDI statements. It also adds a simple
<glossterm>XDI link contract</glossterm>—a data sharing agreement expressed in
XDI—between Alice and Bob.</para>
<programlisting>{
"/$is$ref": [
"(=x-alice)",
"(=!:uuid:x-alice)"
],
"<$iri>": {
"&": "https://xdi.example.com/=!:uuid:x-alice/"
},
"=!:uuid:x-alice": {
"/#friend": [
"=!:uuid:x-bob",
"(=!:uuid:x-alice/#friend)"
],
"/#spouse": [
"=!:uuid:x-david"
],
"[<#email>]<!0>": {
"&": "alice@example.com"
},
"[<#email>]<!1>": {
"&": "asmith@example.net"
},
"<#email>": {
"/$ref": [
"=!:uuid:x-alice[<#email>]<!0>"
]
},
"<#home><#email>": {
"/$ref": [
"=!:uuid:x-alice[<#email>]<!1>"
]
},
"<#work><#email>": {
"/$ref": [
"=!:uuid:x-alice[<#email>]<!1>"
]
}
},
"=!:uuid:x-alice#passport": {
"<#country>": {
"&": "Canada"
},
"<#name>": {
"&": "Alice Smith"
},
"<#number>": {
"&": "1234567"
}
},
"(=!:uuid:x-alice)": {
"/$ref": [
""
]
},
"(=!:uuid:x-alice/#friend)": {
"+!:uuid:x-org#card$do": {
"/$get": [
"=!:uuid:x-alice<#home><#email>"
]
}
},
"(=!:uuid:x-alice/#friend)(+!:uuid:x-org#card$do$if/$true)": {
"{$from}": {
"/$is#friend": [
"=!:uuid:x-alice"
]
}
},
"(=!:uuid:x-bob)": {
"<$iri>": {
"&": "https://xdi.example.com/=!:uuid:x-bob/"
}
}
}</programlisting>
</section>
<section>
<title>The XDI 1.0 Specifications</title>
<para>XDI Core is the first of a series of specifications that will define XDI 1.0. The
following table lists the other planned specifications.</para>
<para>
<table frame="all">
<title>Specifications in the XDI 1.0 Suite</title>
<tgroup cols="2" align="center">
<colspec colname="c1" colnum="1" colwidth="1*"/>
<colspec colname="c2" colnum="2" colwidth="2.4*"/>
<thead>
<row>
<entry>Specification</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>XDI Messaging 1.0</entry>
<entry>Defines the XDI protocol as an abstract pattern for
performing XDI operations using XDI messages</entry>
</row>
<row>
<entry>XDI Bindings 1.0</entry>
<entry>Defines the concrete binding of XDI messaging to specific
transport protocols, beginning with the HTTP(S) protocol</entry>
</row>
<row>
<entry>XDI Connections 1.0</entry>
<entry>Defines the specific XDI protocol for instantiating XDI link
contracts</entry>
</row>
<row>
<entry>XDI Policy 1.0</entry>
<entry>Defines the standard structure and vocabulary of XDI
authorization statements, including XDI link contracts and
policy expressions, so they are portable across all XDI
endpoints</entry>
</row>
<row>
<entry>XDI Discovery 1.0</entry>
<entry>Defines peer-to-peer discovery of XDI endpoint IRI(s) given
an XDI address (or a discoverable identifier that can be
transformed into an XDI address)</entry>
</row>
<row>
<entry>XDI Push 1.0</entry>
<entry>Defines the semantics of XDI link contracts that establish
push relationships between two or more XDI endpoints using the
XDI <code>$push</code> operation</entry>
</row>
<row>
<entry>XDI Dictionary 1.0</entry>
<entry>Defines the semantic rules for XDI dictionary definitions,
including a type dictionary </entry>
</row>
<row>
<entry>XDI Versioning 1.0</entry>
<entry>Defines the semantics for standardized versioning of any XDI
graph or subgraph using the <code>$v</code> versioning
context</entry>
</row>
<row>
<entry>XDI Cryptographic Mechanisms 1.0</entry>
<entry>Defines the standards for digitally signing and encrypting
XDI messages and graphs</entry>
</row>
<row>
<entry>XDI Security Mechanisms 1.0</entry>
<entry>Describes the mechanisms for implementing security in XDI,
including transport-level security, message-level security,
encryption, token formats, etc.</entry>
</row>
<row>
<entry>XDI Privacy Mechanisms 1.0</entry>
<entry>Describes the mechanisms for implementing privacy in XDI,
including privacy-respecting identifiers (e.g., pseudonyms),
privacy-respecting link contracts, data usage controls,
etc.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</section>
<section>
<title> Key Words</title>
<para>The key words <glossterm>MUST</glossterm>, <glossterm>MUST NOT</glossterm>,
<glossterm>REQUIRED</glossterm>, <glossterm>SHALL</glossterm>, <glossterm>SHALL
NOT</glossterm>, <glossterm>SHOULD</glossterm>, <glossterm>SHOULD
NOT</glossterm>, <glossterm>RECOMMENDED</glossterm>, <glossterm>MAY</glossterm>,
and <glossterm>OPTIONAL</glossterm> are to be interpreted as described in <xref
linkend="rfc2119"/>.</para>
</section>
<section>
<title>Normative References</title>
<bibliolist>
<bibliomixed id="xdi-messaging-1.0">
<abbrev>OASIS-XDI-Messaging-V1.0</abbrev>
<date>&pubdate; </date>
<title><ulink url="../../xdi-messaging-1.0/xdi-messaging-1.0-wd01.xml">OASIS XDI
1.0 Messaging Specification</ulink></title>
<author>
<firstname>Markus </firstname>
<surname>Sabadello</surname>
</author>, <author>
<firstname>Drummond </firstname>
<surname>Reed</surname>
</author>. <releaseinfo>OASIS &standard;. </releaseinfo>
<citetitle><ulink url="&latest-loc;/xdi-messaging.html"
>&latest-loc;/xdi-messaging.html</ulink>.</citetitle>
</bibliomixed>
<bibliomixed id="xdi-bindings-1.0">
<abbrev>OASIS-XDI-Binding-V1.0</abbrev>
<date>&pubdate; </date>
<title><ulink url="../../xdi-bindings-1.0/xdi-bindings-1.0-wd01.xml">OASIS XDI
1.0 Bindings Specification</ulink></title>
<author>
<firstname>Markus </firstname>
<surname>Sabadello</surname>
</author>, <author>
<firstname>Drummond </firstname>
<surname>Reed</surname>
</author>. <releaseinfo>OASIS &standard;. </releaseinfo>
<citetitle><ulink url="&latest-loc;/xdi-bindings.html"
>&latest-loc;/xdi-bindings.html</ulink>.</citetitle>
</bibliomixed>
<bibliomixed id="xdi-discovery-1.0">
<abbrev>OASIS-XDI-Discovery-V1.0</abbrev>
<date>&pubdate; </date>
<title><ulink url="../../xdi-discovery-1.0/xdi-discovery-1.0-wd01.xml">OASIS XDI
1.0 Discovery Specification</ulink></title>
<author>
<firstname>Markus </firstname>
<surname>Sabadello</surname>
</author>, <author>
<firstname>Drummond </firstname>
<surname>Reed</surname>
</author>. <releaseinfo>OASIS &standard;. </releaseinfo>
<citetitle><ulink url="&latest-loc;/xdi-discovery.html"
>&latest-loc;/xdi-discovery.html</ulink>.</citetitle>
</bibliomixed>
<bibliomixed id="xdi-dictionary-1.0">
<abbrev>OASIS-XDI-Dictionary-V1.0</abbrev>
<date>&pubdate; </date>
<title><ulink url="../../xdi-dictionary-1.0/xdi-dictionary-1.0-wd01.xml">OASIS
XDI 1.0 Dictionary Specification</ulink></title>
<author>
<firstname>Markus </firstname>
<surname>Sabadello</surname>
</author>, <author>
<firstname>Drummond </firstname>
<surname>Reed</surname>
</author>. <releaseinfo>OASIS &standard;. </releaseinfo>
<citetitle><ulink url="&latest-loc;/xdi-dictionary.html"
>&latest-loc;/xdi-dictionary.html</ulink>.</citetitle>
</bibliomixed>
<bibliomixed id="xdi-policy-1.0">
<abbrev>OASIS-XDI-Policy-V1.0</abbrev>
<date>&pubdate; </date>
<title><ulink url="../../xdi-policy-1.0/xdi-policy-1.0-wd01.xml">OASIS XDI 1.0
Policy Specification</ulink></title>
<author>
<firstname>Markus </firstname>
<surname>Sabadello</surname>
</author>, <author>
<firstname>Drummond </firstname>
<surname>Reed</surname>
</author>. <releaseinfo>OASIS &standard;. </releaseinfo>
<citetitle><ulink url="&latest-loc;/xdi-policy.html"
>&latest-loc;/xdi-privacy.html</ulink>.</citetitle>
</bibliomixed>
<bibliomixed id="xdi-security-1.0">
<abbrev>OASIS-XDI-Security-V1.0</abbrev>
<date>&pubdate; </date>
<title><ulink url="../../xdi-security-1.0/xdi-security-1.0-wd01.xml">OASIS XDI
1.0 Security Mechanisms Specification</ulink></title>
<author>
<firstname>Markus </firstname>
<surname>Sabadello</surname>
</author>, <author>
<firstname>Drummond </firstname>
<surname>Reed</surname>
</author>. <releaseinfo>OASIS &standard;. </releaseinfo>
<citetitle><ulink url="&latest-loc;/xdi-security.html"
>&latest-loc;/xdi-security.html</ulink>.</citetitle>
</bibliomixed>
<bibliomixed id="xdi-privacy-1.0">
<abbrev>OASIS-XDI-Privacy-V1.0</abbrev>
<date>&pubdate; </date>
<title><ulink url="../../xdi-privacy-1.0/xdi-privacy-1.0-wd01.xml">OASIS XDI 1.0
Privacy Mechanisms Specification</ulink></title>
<author>
<firstname>Markus </firstname>
<surname>Sabadello</surname>
</author>, <author>
<firstname>Drummond </firstname>
<surname>Reed</surname>
</author>. <releaseinfo>OASIS &standard;. </releaseinfo>
<citetitle><ulink url="&latest-loc;/xdi-privacy.html"
>&latest-loc;/xdi-messaging.html</ulink>.</citetitle>
</bibliomixed>
<bibliomixed id="rdf-concepts">
<abbrev>rdf-concepts</abbrev><date>25 February 2014</date>
<title><ulink url="http://www.w3.org/TR/rdf11-concepts">RDF 1.1 Concepts and
Abstract Syntax</ulink></title>
<author>
<firstname>Richard </firstname>
<surname>Cyganiak</surname>
</author>, <author>
<firstname>David </firstname>
<surname>Wood</surname>
</author>, <author>
<firstname>Markus </firstname>
<surname>Lanthaler</surname>
</author>. <releaseinfo>W3C Recommendation 25 February 2014 </releaseinfo>
</bibliomixed>
<bibliomixed id="rdf-datasets">
<abbrev>rdf-datasets</abbrev><date>25 February 2014</date>
<title><ulink url="http://www.w3.org/TR/rdf11-datasets">RDF 1.1: On Semantics of
RDF Datasets</ulink></title>
<author>
<firstname>Antoine </firstname>
<surname>Zimmerman</surname>
</author>. <releaseinfo>W3C Working Group Note 25 February 2014 </releaseinfo>
</bibliomixed>
<bibliomixed id="rdf-schema">
<abbrev>rdf-schema</abbrev><date>25 February 2014</date>
<title><ulink url="http://www.w3.org/TR/rdf-schema">RDF 1.1
Schema</ulink></title>
<author>
<firstname>Dan </firstname>
<surname>Brickley</surname>
</author>, <author>
<firstname>R.V. </firstname>
<surname>Guha</surname>
</author>. <releaseinfo>W3C Recommendation 25 February 2014 </releaseinfo>
</bibliomixed>
<bibliomixed id="owl">
<abbrev>owl</abbrev><date>11 December 2012</date>
<title><ulink url="http://www.w3.org/TR/owl2-overview/">OWL 2 Web Ontology
Language Document Overview</ulink></title>
<releaseinfo>W3C Recommendation 11 December 2012 </releaseinfo>
</bibliomixed>
<bibliomixed id="rfc2119">
<abbrev>RFC 2119</abbrev><date>March 1997</date>
<title><ulink url="http://www.ietf.org/rfc/rfc2119.txt">Key words for use in
RFCs to Indicate Requirement Levels</ulink></title>
<author>
<firstname>S. </firstname>
<surname>Bradner</surname>
</author>. <releaseinfo>IETF (Internet Engineering Task Force)</releaseinfo>
</bibliomixed>
<bibliomixed id="rfc2234">
<abbrev>RFC 2234</abbrev><date>November 1997</date>
<title><ulink url="http://www.ietf.org/rfc/rfc2234.txt">Augmented BNF for Syntax
Specifications: ABNF</ulink></title>
<author>
<firstname>D. </firstname>
<surname>Crocker</surname>
</author>, <author>
<firstname>P. </firstname>
<surname>Overell</surname>
</author>. <releaseinfo>IETF (Internet Engineering Task Force)</releaseinfo>
</bibliomixed>
<bibliomixed id="rfc3987">
<abbrev>RFC 3987</abbrev><date>January 2005</date>
<title><ulink url="http://www.ietf.org/rfc/rfc3987.txt">IRI</ulink></title>
<author>
<firstname>M. </firstname>
<surname>Duerst</surname>
</author>. <author>
<firstname>M. </firstname>
<surname>Suignard</surname>
</author>. <releaseinfo>IETF (Internet Engineering Task Force)</releaseinfo>
</bibliomixed>
<bibliomixed id="rfc4627">
<abbrev>RFC 4627</abbrev><date>July 2006</date>
<title><ulink url="http://www.ietf.org/rfc/rfc4627.txt">The application/json
Media Type for JavaScript Object Notation (JSON)</ulink></title>
<author>
<firstname>D. </firstname>
<surname>Crockford</surname>
</author>. <releaseinfo>IETF (Internet Engineering Task Force)</releaseinfo>
</bibliomixed>
<bibliomixed id="rfc4122">
<abbrev>RFC 4122</abbrev><date>July 2005</date>
<title><ulink url="http://www.ietf.org/rfc/rfc4122.txt">A Universally Unique
IDentifier (UUID) URN Namespace</ulink></title>
<author>
<firstname>D. </firstname>
<surname>Crockford</surname>
</author>. <releaseinfo>IETF (Internet Engineering Task Force)</releaseinfo>
</bibliomixed>
<!--bibliomixed id="rfc5952">
<abbrev>RFC 5952</abbrev><date>August 2010</date>
<title><ulink url="http://www.ietf.org/rfc/rfc5952.txt">A Recommendation for
IPv6 Address Text Representation</ulink></title>
<author>
<firstname>S. </firstname>
<surname>Kawamura</surname>
</author>, <author>
<firstname>M. </firstname>
<surname>Kawashima</surname>
</author>. <releaseinfo>IETF (Internet Engineering Task Force)</releaseinfo>
</bibliomixed-->
<bibliomixed id="rfc7159">
<abbrev>RFC 7159</abbrev><date>March 2014</date>
<title><ulink url="http://rfc7159.net/rfc7159">The JavaScript Object Notation
(JSON) Data Interchange Format</ulink></title>
<author>
<firstname>T. </firstname>
<surname>Bray</surname>
</author>. <releaseinfo>IETF (Internet Engineering Task Force)</releaseinfo>
</bibliomixed>
<bibliomixed id="ecma-404">
<abbrev>ECMA-404</abbrev><date>October 2013</date>
<title><ulink
url="http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf"
>The JSON Data Interchange Format</ulink></title>
<author>
<firstname>S. </firstname>
<surname>Kawamura</surname>
</author>, <author>
<firstname>M. </firstname>
<surname>Kawashima</surname>
</author>. <releaseinfo>IETF (Internet Engineering Task Force)</releaseinfo>
</bibliomixed>
<bibliomixed id="unicode-tr15">
<abbrev>UAX15</abbrev><date>June 2015</date>
<title><ulink url="http://unicode.org/reports/tr31/">Unicode Normalization
Forms</ulink></title>
<author>
<firstname>Mark </firstname>
<surname>Davis</surname>
</author>, <author>
<firstname>Ken </firstname>
<surname>Whistler</surname>
</author>. <releaseinfo>Unicode Consortium</releaseinfo>
</bibliomixed>
<bibliomixed id="unicode-tr31">
<abbrev>UAX31</abbrev><date>June 2015</date>
<title><ulink url="http://unicode.org/reports/tr31/">Unicode Identifier and
Pattern Syntax</ulink></title>
<author>
<firstname>Mark </firstname>
<surname>Davis</surname>
</author>. <releaseinfo>Unicode Consortium</releaseinfo>
</bibliomixed>
<!--bibliomixed id="fips180-4">
<abbrev>FIPS 180-4</abbrev><date>March 2012</date>
<title><ulink
url="http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf"
>Secure Hash Standard (SHS)</ulink></title>
<author>
<firstname/>
<surname/>
</author>
<releaseinfo>Federal Information Processing Standards Publication (FIPS),
NIST</releaseinfo>
</bibliomixed-->
</bibliolist>
</section>
<section>
<title>Non-Normative References</title>
<bibliolist>
<bibliomixed id="erm">
<abbrev>erm</abbrev><date>1976</date>
<title><ulink url="https://en.wikiversity.org/wiki/1976/Chen">The
Entity-Relationship Model: Toward a Unified View of Data</ulink></title>
<author>
<firstname>Peter </firstname>
<surname>Chen</surname>
</author>. <releaseinfo>ACM Transactions on Database Systems 1(1): 9–36.
doi:10.1145/320434.320440</releaseinfo>
</bibliomixed>
<bibliomixed id="uml">
<abbrev>uml</abbrev><date>1 March 2015</date>
<title><ulink url="http://www.omg.org/spec/UML/2.5/">UML 2.5
Specifications</ulink></title>
</bibliomixed>
<bibliomixed id="webarch">
<abbrev>webarch</abbrev><date>15 December 2004</date>
<title><ulink url="http://www.w3.org/TR/webarch/#id-resources">Architecture of
the World Wide Web, Volume One</ulink></title>
<author>
<firstname>Ian </firstname>
<surname>Jacobs</surname>
</author>, <author>
<firstname>Norman </firstname>
<surname>Walsh</surname>
</author>. <releaseinfo>W3C Recommendation</releaseinfo>
</bibliomixed>
<bibliomixed id="httprange14">
<abbrev>httprange14</abbrev>
<title><ulink url="http://en.wikipedia.org/wiki/HTTPRange-14"
>HTTPRange-14</ulink></title>
<releaseinfo>Wikipedia</releaseinfo>
</bibliomixed>
<bibliomixed id="reification">
<abbrev>reification</abbrev>
<title><ulink url="http://en.wikipedia.org/wiki/Reification_(computer_science)"
>Reification (computer science)</ulink></title>
<releaseinfo>Wikipedia</releaseinfo>
</bibliomixed>
<bibliomixed id="zooko">
<abbrev>zooko</abbrev>
<title><ulink url="http://en.wikipedia.org/wiki/Zooko's_triangle">Zooko's
triangle</ulink></title>
<releaseinfo>Wikipedia</releaseinfo>
</bibliomixed>
<bibliomixed id="sovereign-identity">
<abbrev>sovereign-identity</abbrev>
<title><ulink
url="http://blogs.law.harvard.edu/doc/2013/10/14/iiw-challenge-1-sovereign-identity-in-the-great-silo-forest/"
>Sovereign Identity in the Great Silo Forest</ulink></title>
<releaseinfo>Doc Searls Weblog</releaseinfo>
</bibliomixed>
<bibliomixed id="pbd">
<abbrev>pbd</abbrev>
<title><ulink url="https://www.privacybydesign.ca">Privacy by
Design</ulink></title>
<releaseinfo>Privacy by Design</releaseinfo>
</bibliomixed>
<bibliomixed id="json-ld">
<abbrev>json-ld</abbrev><date>16 January 2014</date>
<title><ulink url="http://www.w3.org/TR/json-ld/">JSON-LD 1.0: A JSON-based
Serialization for Linked Data</ulink></title>
<author>
<firstname>Manu </firstname>
<surname>Sporny</surname>
</author>, <author>
<firstname>Dave </firstname>
<surname>Longley</surname>
</author>, <author>
<firstname>Gregg </firstname>
<surname>Kellogg</surname>
</author>, <author>
<firstname>Markus </firstname>
<surname>Lanthaler</surname>
</author>, <author>
<firstname>Niklas </firstname>
<surname>Lindström</surname>
</author>. <releaseinfo>W3C Recommendation 16 January 2014</releaseinfo>
</bibliomixed>
<bibliomixed id="ldplatform">
<abbrev>ldplatform</abbrev><date>26 February 2015</date>
<title><ulink url="http://www.w3.org/TR/ldp/">Linked Data Platform 1.0</ulink></title>
<author>
<firstname>Steve </firstname>
<surname>Speicher</surname>
</author>, <author>
<firstname>John </firstname>
<surname>Arwe</surname>
</author>, <author>
<firstname>Ashok </firstname>
<surname>Malhotra</surname>
</author>. <releaseinfo>W3C Recommendation 26 February 2015</releaseinfo>
</bibliomixed>
<bibliomixed id="jsonpath">
<abbrev>jsonpath</abbrev>
<title><ulink url="http://goessner.net/articles/JsonPath/">JSON
Path</ulink></title>
</bibliomixed>
</bibliolist>
<para/>
</section>
</section>
<section>
<title>Design Goals</title>
<para>This section communicates the design goals that have guided the development of
XDI.</para>
<section id="addressability">
<title>100% Addressability of All Graph Nodes</title>
<para>To perform semantic data interchange with precise control over every data element,
the first requirement of the XDI TC was that every node of every XDI graph be
uniquely addressable. This architecture essentially mirrors that of the W3C in the
Architecture of the World Wide Web, where it states: <quote>"To benefit from and
increase the value of the World Wide Web, agents should provide URIs as
identifiers for resources."</quote></para>
<para>This requirement is one reason the XDI TC does not use the term “XDI document” or
compare XDI graphs to documents. A document metaphor suggests a natural division
between addressing of the document and addressing of nodes inside the document. In
Web URI architecture, this is reflected by the # fragment, which represents an
address local to the current resource, vs. an address outside this resource.</para>
<para>The XDI graph model does not have this distinction because every node of every XDI
graph is equally addressable. (Or, as members of the XDI TC have put it, “It’s
turtles all the way down.”)</para>
<para>Note that XDI addressing stops once you reach an XDI literal node—the ultimate
leaf nodes of an XDI graph which contain the literal data values. If a client needs
to address within a literal data value, it must switch from an XDI address to an
address in the native addressing syntax of the literal data (e.g., a JSON path for a
JSON document, an XML path for an XML document, a fragment for an HTML document,
etc.) Such addresses are out of scope for XDI.</para>
<para>This requirement is perhaps the most significant difference between XDI and RDF,
because unique addressability of RDF graph nodes was not part of the RDF problem
domain. This is explained in more detailed in the paper <glossterm>How XDI Builds on
RDF</glossterm> cited in the Introduction.</para>
</section>
<section id="heterarchical">
<title>Heterarchical — No Central Authority</title>
<para>A second core design goal of XDI architecture is to support heterarchy, i.e., to
not assume or rely on a central authority. This requires designing a peer-to-peer
model in which any group of peers may cooperate to create an addressing and
interchange space for its community. This addressing space may make use of existing
resolvable identifiers for those peers, or it may extend those existing addresses,
or it may be an entirely new addressing space. In all cases XDI can standardize
discovery of peers and peer addresses, including both public and private discovery.
This “radically P2P” architecture supports any deployment topology, from highly
centralized to highly decentralized, and imposes the fewest pre-existing policy
assumptions or restrictions on communities of XDI users.</para>
<para>Note: for more about this aspect of XDI, see the XDI Discovery specification.
<xref linkend="xdi-discovery-1.0"/></para>
</section>
<section>
<title id="contextual">Contextual Identification</title>
<para>It is a mantra in digital identity that “identity is contextual”, i.e., that both
the requirements for identification and the uniqueness of identifiers is relative to
the context in which identification is required. Even “global” or “absolute”
identifiers like telephone numbers, email addresses, or URIs are still relative to a
particular addressing context.</para>
<para>It is also a maxim in the privacy community that “privacy is contextual”, and thus
a data authority must be able to control the data being shared and permissions being
granted in any identification context.</para>
<para>This primacy of context means that a third core XDI design goal is that it support
the ability to model context at any degree of granularity and to enable XDI
authorities to control the sharing of identity and data by context.</para>
<para>Again, we note that modeling of context was not a requirement of the RDF problem
domain, so this has not been an aspect of digital identity or data sharing addressed
by the RDF graph model. This topic is discussed in greater depth in the
<glossterm>How XDI Builds on RDF paper</glossterm>.</para>
</section>
<section id="persistent">
<title>Persistent Identification</title>
<para>A second core quality of identification is whether it is persistent (immutable) or
reassignable (mutable). In the former case, an identifier (or other means of
identification) is bound to the resource being identified in such a way that this
association will not change over time—ideally forever. In the latter case, an
identifier bound to one resource at one point in time (such as an IP address
assigned to one computer, or a domain name registered to one owner) may subsequently
be bound to a different resource at another point in time (such as when an IP
address is reassigned to a new computer, or when a domain name is transferred to a
new owner).</para>
<para>In the context of digital identity and secure data sharing, persistent
identification is a requirement for one core reason: if an XDI authority with a
particular identifier has been granted a specific set of permissions, and the XDI
authority identified by that identifier changes, then those permissions now belong
to (and can be exercised by) a different authority.</para>
<para>Persistent identification is also important for identity and data portability (see
below), because if an identifier (or other means of identification) needs to change
when the location of an XDI graph changes, the XDI relationships described in that
XDI graph will break. For these reasons, it is critical that XDI syntactically
distinguish a class of identifiers that XDI authorities can agree will be assigned
once to a resource and never be reassigned to another resource.</para>
<para>At the same time, it is widely acknowledged that persistent identification is a
usability nightmare. The human brain is wired to use simple, memorable natural
language identifiers for our cognition and communication, and we subconsciously
adjust the mappings of those identifiers over time as we learn, grow, and evolve.
For example, the person you first think of by the name “Mary” today may be different
from the person you first thought of by that name when you were a child.</para>
<para>So a key design goal of XDI is to support the requirements of both persistent and
reassignable forms of identification; to provide precise means to map between them;
and to make it syntactically unambiguous which form is being used in which
context.</para>
</section>
<section id="serialization">
<title>Serialization Independence</title>
<para>Another goal is for the XDI graph model to be a precise logical abstract model
that is independent of any specified serialization format. For example, the XDI 1.0
specifications specify two display formats and one JSON serialization format. In
addition the XDI TC plans to specify at least one XML serialization format. All
these formats transmit 100% of the information in an XDI graph, and all must be
losslessly convertible into the others.</para>
</section>
<section id="portability">
<title>Portability and Location Independence</title>
<para>Since XDI graphs may be used to describe any data associated with any entity,
including people and businesses that are constantly changing contexts, attributes,
service providers, and endpoints on the network, another design goal is for the
semantics expressed in an XDI graph to be portable, i.e., location-independent. This
means an XDI graph may be moved to any location (endpoint) on a network without
breaking any of the descriptions or relations described in the graph.</para>
<para>This design goal is particularly important for XDI graphs representing
individuals, as it supports the ability for an individual to maintain ongoing,
sustainable control of his/her personal digital identity, data and relationships,
independent of any particular service provider or network location.</para>
<para>Note: the specialized use of the XDI protocol to provide wide-area location
independence is defined in the XDI Discovery specification. <xref