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
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
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.
Nottingham & Beckett Expires January 1, 2009 [Page 1]
Internet-Draft AtomTriples June 2008
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
Nottingham & Beckett Expires January 1, 2009 [Page 2]
Internet-Draft AtomTriples June 2008
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.
Nottingham & Beckett Expires January 1, 2009 [Page 3]
Internet-Draft AtomTriples June 2008
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
Nottingham & Beckett Expires January 1, 2009 [Page 4]
Internet-Draft AtomTriples June 2008
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.
Nottingham & Beckett Expires January 1, 2009 [Page 5]
Internet-Draft AtomTriples June 2008
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>
Nottingham & Beckett Expires January 1, 2009 [Page 6]
Internet-Draft AtomTriples June 2008
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/
Nottingham & Beckett Expires January 1, 2009 [Page 7]
Internet-Draft AtomTriples June 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Nottingham & Beckett Expires January 1, 2009 [Page 8]