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Network Working Group                                      M. Nottingham
Internet-Draft                                                D. Beckett
Intended status: Informational                             June 30, 2008
Expires: January 1, 2009


             AtomTriples: Embedding RDF Statements in Atom
                    draft-nottingham-atomtriples-00

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   This Internet-Draft will expire on January 1, 2009.

Abstract

   This specification describes AtomTriples, a set of Atom extension
   elements for embedding RDF statements in Atom documents (both element
   and feed), and declaring how they can be derived from existing
   content.











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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . . . 3
   3.  Embedded Statements . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  The at:md Element . . . . . . . . . . . . . . . . . . . . . 4
     3.2.  The subject Attribute . . . . . . . . . . . . . . . . . . . 4
   4.  Derived Statements  . . . . . . . . . . . . . . . . . . . . . . 4
     4.1.  The at:feedmap Element  . . . . . . . . . . . . . . . . . . 5
     4.2.  The at:entrymap Element . . . . . . . . . . . . . . . . . . 5
     4.3.  The at:map Element  . . . . . . . . . . . . . . . . . . . . 5
   5.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8

































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1.  Introduction

   This specification describes AtomTriples, a set of Atom [RFC4287]
   extension elements for embedding RDF
   [W3C.WD-rdf-syntax-grammar-20031010] statements in Atom documents
   (both element and feed), as well as declaring how they can be derived
   from existing content.

   Statements can be embedded directly as RDF/XML using the at:md
   element at the feed or entry level.  Additionally, a feed can declare
   that specific Atom elements (or extensions) can be parsed into RDF
   statements using the at:feedmap element (for metadata attached to a
   feed) or an at:entrymap element (for metadata attached to entries).

   The semantics of a property that appears in both places (e.g., in a
   feed-level at:md as well as derived from a at:feedmap) is undefined;
   presumably, they would be added to the model as two separate
   statements.

   Likewise, the mechanics of combining metadata from multiple instances
   of the same entry, or from multiple feed documents, is out of the
   scope of this specification.


2.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   All XML elements in this specification use the the namespace URI
   [W3C.REC-xml-names-19990114]
   "http://purl.org/syndication/atomtriples/1".  In this document, that
   URI is mapped to the "at" prefix.

   Unless specified otherwise, AtomTriples elements MAY contain foreign
   markup, which SHOULD be handled according as it is in the Atom
   syndication format.


3.  Embedded Statements

   RDF statements can be directly embedded in Atom feeds and entries as
   RDF/XML using the at:md element.







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3.1.  The at:md Element

   The at:md element MAY occur as a child of atom:feed or atom:entry,
   and contains any number of RDF statements which MUST serialised as
   RDF/XML.  It MAY occur in a given context any number of times.

   The subject of these statements is, by default, the value of the
   atom:id element in the same context (atom:element or atom:feed).
   However, this behaviour MAY be overridden by specifying the subject
   attribute.

   After the subject is determined, the contents SHOULD be processed as
   a propertyEltList in [W3C.WD-rdf-syntax-grammar-20031010].

3.2.  The subject Attribute

   When present, the subject attribute indicates how to derive the RDF
   subject of statements sourced from the element it is attached to.

   It MUST contain a URI which MUST be interpreted as a link relation;
   the first such occurrence of an atom:link element in the same context
   as its parent element with that relation (in lexical order) will
   indicate the URI to use as the subject.

   For example,

     <entry>
       <title>Atom-Powered Robots Run Amok</title>
       <link href="http://example.org/2003/12/13/atom03"/>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
       <updated>2003-12-13T18:30:02Z</updated>
       <summary>Some text.</summary>
       <at:md subject="alternate">
          <!-- .. -->
       </at:md>
     </entry>

   indicates that the subject of statements in this entry is
   "http://example.org/2003/12/13/atom03" (because Atom links default to
   the "alternate" relation).

   This specification does not define the semantics of the subject
   attribute when a suitable link cannot be found.


4.  Derived Statements

   Atom documents can declare mappings of existing content to RDF



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   statements using the at:feedmap and at:entrymap elements.

4.1.  The at:feedmap Element

   The at:feedmap element MAY occur as a child of atom:feed, and MUST
   NOT occur more than once.  It MAY contain any number of at:map
   elements which indicate mappings for feed-level element contents to
   statements, within the scope of the feed document it occurs in.

4.2.  The at:entrymap Element

   The at:entrymap element MAY occur as a child of atom:feed, and MAY
   occur as the child of atom:entry in an Atom Entry Document.  It MUST
   NOT occur more than once, and MAY contain any number of at:map
   elements which indicate mappings for entry-level element contents to
   statements, within the scope of the document it occurs in.

4.3.  The at:map Element

   The at:map element indicates how an element in a given context
   (either feed or entry, depending on use) maps to RDF statements.  Its
   content MUST be an XML QName, and indicates the element that is being
   mapped.  It MUST have a property attribute that MUST be a URI, which
   associates the element in the appropriate context with the given RDF
   property.

   For example,

   <at:map
    property="http://purl.org/dc/elements/1.1/title">atom:title</at:map>

   indicates that the atom:title element's content should be mapped to
   the http://purl.org/dc/elements/1.1/title property.  Given the entry

   <atom:entry>
    <atom:id>http://example.com/a</atom:id>
    <atom:title>Test</atom:title>
   </atom:entry>

   and the map above as a child of at:entrymap, the following triple
   would be implied;

 <http://example.com/a> <http://purl.org/dc/elements/1.1/title> "Test" .

   The exact URI to use as the subject of the statements derived by
   mapping is, by default, the value of the atom:id element in the same
   context.  However, this behaviour MAY be overridden by specifying the
   subject attribute.



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   By default, the content of the given element will be converted to an
   RDF Literal if it contains no markup, and to an XML Literal if it
   does.  This behaviour may be modified by future revisions of this
   specification.


5.  Example

<feed xmlns="http://www.w3.org/2005/Atom"
   xmlns:at="http://purl.org/syndication/atomtriples/1">
  <title>Example Feed</title>
  <link href="http://example.org/"/>
  <updated>2003-12-13T18:30:02Z</updated>
  <author>
    <name>John Doe</name>
  </author>
  <id>urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6</id>
  <at:md>
    <!-- This is feed-level metadata in plain RDF/XML -->
    <!-- @about defaults to atom:id; can be overridden with @subject -->
    <!-- xml base is available and applies, as per RDF -->
  </at:md>
  <at:feedmap>
   <!-- How to map feed-level RDF statements into Atom metadata -->
   <at:map property="http://dc.org/#title">atom:title</at:map>
  </at:feedmap>
  <at:entrymap>
   <!-- entry-level mapping -->
   <at:map property="http://dc.org/#title"
               subject="alternate">atom:title</at:map>
  </at:entrymap>

  <entry>
    <title>Atom-Powered Robots Run Amok</title>
    <link href="http://example.org/2003/12/13/atom03"/>
    <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
    <updated>2003-12-13T18:30:02Z</updated>
    <summary>Some text.</summary>
    <at:md>
       <!-- this is entry-level metadata in plain RDF/XML -->
       <!-- @about defaults to atom:id;
            can be overridden with @subject -->
       <!-- xml base is available and applies, as per RDF -->
    </at:md>
  </entry>
</feed>





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6.  Security Considerations

   The security considerations for these extensions are the union of
   those that apply to processing both Atom and RDF.


7.  IANA Considerations

   This document has no actions for IANA.


8.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4287]  Nottingham, M. and R. Sayre, "The Atom Syndication
              Format", RFC 4287, December 2005.

   [W3C.REC-xml-names-19990114]
              Bray, T., Hollander, D., and A. Layman, "Namespaces in
              XML", W3C REC REC-xml-names-19990114, January 1999.

   [W3C.WD-rdf-syntax-grammar-20031010]
              Beckett, D., "RDF/XML Syntax Specification (Revised)", W3C
              LastCall WD-rdf-syntax-grammar-20031010, October 2003.


Appendix A.  Acknowledgements

   The authors would like to thank Hong Zhang for his help and feedback;
   they take all responsibility for errors and omissions.


Authors' Addresses

   Mark Nottingham

   Email: mnot@pobox.com
   URI:   http://www.mnot.net/


   Dave Beckett

   Email: dave@dajobe.org
   URI:   http://www.dajobe.org/





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