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Network Working Group                                           N. Mehta
Internet-Draft                                              Oracle Corp.
Intended status: Experimental                              June 29, 2009
Expires: December 31, 2009


                     In-lining Extensions for Atom
                       draft-mehta-atom-inline-01

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Abstract

   This specification defines mechanisms for in-lining representations
   of linked Atom resources.




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Editorial Note

   To provide feedback on this Internet-Draft, join the atom-syntax
   mailing list (http://www.imc.org/atom-syntax/) [1].


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Namespace . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.2.  Notational Conventions  . . . . . . . . . . . . . . . . . . 3
     1.3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  In-line Representation of Atom Resources  . . . . . . . . . . . 3
     2.1.  The "ae:inline" Extension Element . . . . . . . . . . . . . 4
       2.1.1.  The "type" Attribute  . . . . . . . . . . . . . . . . . 4
       2.1.2.  Empty "ae:inline" Element . . . . . . . . . . . . . . . 4
   3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     3.1.  Feed with empty in-line replies feed link . . . . . . . . . 4
     3.2.  Entry with in-line via feed link  . . . . . . . . . . . . . 5
     3.3.  Entry with in-line up link  . . . . . . . . . . . . . . . . 5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     5.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     5.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 7
   Appendix B.  Revision History . . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7
























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1.  Introduction

   This document defines an extension for in-line representations of
   linked Atom resources within the Atom Syndication Format [RFC4287].

1.1.  Namespace

   The XML Namespaces URI for the XML data format described in this
   specification is:

       http://purl.org/atom/ext/

   This specification uses the prefix "ae:" for the namespace name.  The
   prefix "atom:" is used for "http://www.w3.org/2005/Atom", the
   namespace name of the Atom Syndication Format [RFC4287].  These
   namespace prefixes are not semantically significant.

1.2.  Notational Conventions

   Some sections of this specification are illustrated with fragments of
   a non-normative RELAX NG Compact schema [RELAXNG].  In those
   sections, this specification uses the atomEntry, atomFeed, and
   atomCommonAttributes, defined in [RFC4287].

   However, the text of this specification provides the definition of
   conformance.

   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 [RFC2119].

1.3.  Terminology

   This specification uses Atom link relations to identify different
   types of links; see the Atom specification [RFC4287] for information
   about their syntax, and the IANA link relation registry for more
   information about specific values.


2.  In-line Representation of Atom Resources

   Some applications require the ability to pre-fetch resources linked
   from an Atom document using the atom:link element [RFC4287].  Such
   in-line representations are similar to the in-line content model of
   Atom.

   An Atom document MAY include the in-line representation of a linked
   Atom resource by using the ae:inline element inside the corresponding



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   atom:link element.  The in-lined representation is only a hint and
   MAY differ from the representation obtained from the URI referenced
   in the link.  Atom Processors SHOULD use the link URI to obtain the
   complete representation of the linked resource.

2.1.  The "ae:inline" Extension Element

   The "ae:inline" element contains an approximate representation of the
   linked resource.



   extensionInline =
      element ae:inline {
         atomCommonAttributes,
         atomFeed | atomEntry | empty
      }

2.1.1.  The "type" Attribute

   The type attribute on a link element is a hint about the type of
   representation that is expected to be returned when the value of the
   href attribute is dereferenced.  A processor must be prepared to deal
   with either Atom document type regardless of the value of the type
   attribute in the link element.

2.1.2.  Empty "ae:inline" Element

   The ae:inline element may be empty if the producer of the Atom
   document a linked resource cannot be in-lined, e.g., due to
   inadequate authorization or if the resource does not yet exist.


3.  Examples

3.1.  Feed with empty in-line replies feed link

   The following example demonstrates use of an empty in-lined feed
   within an atom:link element.  The type attribute of link is
   interpreted as an Atom feed document due to the requirements of the
   replies link relation.










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   <feed xmlns="http://www.w3.org/2005/Atom"
            xmlns:thr="http://purl.org/syndication/thread/1.0">
       <id>http://www.example.org/entries</id>
       <title>My posts</title>
       <updated>2006-03-01T12:12:12Z</updated>
       <link rel="replies"
         href="http://www.example.org/replies">
         <ae:inline xmlns:ae="http://purl.org/atom/ext/"/>
       </link>
       <link rel="self"
         href="http://www.example.org/entries" />
       ...
   </feed>

3.2.  Entry with in-line via feed link

   The following example demonstrates use of an in-lined feed within an
   atom:link element.  The type attribute of link is general enough to
   allow either Atom feed or entry document to be in-lined.

   <entry xmlns="http://www.w3.org/2005/Atom"
            xmlns:thr="http://purl.org/syndication/thread/1.0">
       <id>http://www.example.org/entry/1</id>
       <title>My posts</title>
       <updated>2006-03-01T12:12:12Z</updated>
       <link rel="via" type="application/atom+xml"
         href="http://www.example.org/entry/1/via">
         <ae:inline
           xmlns:ae="http://purl.org/atom/ext/"
           xmlns:thr="http://purl.org/syndication/thread/1.0">
           <feed>
           ...
           </feed>
         </ae:inline>
       </link>
       <link rel="self"
         href="http://www.example.org/entry/1" />
       ...
   </entry>

3.3.  Entry with in-line up link

   The following example demonstrates use of an in-lined entry within an
   atom:link element.  The type attribute of link is specifically
   limiting the in-lined content to use an Atom entry document.






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 <entry xmlns="http://www.w3.org/2005/Atom">
   <link rel="up" type="application/atom+xml;type=entry"
     href="/finance/feeds/default/portfolios/1">
     <ae:inline>
       <entry>
          ...
       </entry>
     </ae:inline>
   </link>
   <link rel="edit"
      href="/finance/feeds/default/portfolios/1/positions/NASDAQ:ORCL"/>
   ...
 </entry>


4.  Security Considerations

   In-line Extensions for Atom are subject to the security
   considerations found in Section 8 of [RFC4287].

   In-line representations can overwhelm Atom processors.  For this
   reason, consumers of Atom representations should take adequate
   precautions to limit resource consumption when processing ae:inline
   elements.


5.  References

5.1.  Normative References

   [HTML]     Raggett, D., Hors, A., and I. Jacobs, "HTML 4.01
              Specification, W3C REC REC-html401-19991224",
              December 1999,
              <http://www.w3.org/TR/1999/REC-html401-19991224>.

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

   [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.

   [RFC3548]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 3548, July 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.




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

   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [W3C.REC-XHTML]
              Pemberton, S., "XHTML 1.0: The Extensible HyperText Markup
              Language", W3C REC-XHTML, January 2000,
              <http://www.w3.org/TR/xhtml1/>.

5.2.  Informative References

   [RELAXNG]  Clark, J., "RELAX NG Compact Syntax", December 2001, <http
              ://www.oasis-open.org/committees/relax-ng/
              compact-20021121.html>.

URIs

   [1]  <http://www.imc.org/atom-syntax/>


Appendix A.  Acknowledgements

   On the atom-syntax mailing list, Hadrien Gardeur, Al Brown, Julian
   Reschke, Mark Nottingham, Pablo Castro, Kyle Marvin, and James Snell
   provided very valuable feedback to solidify this draft.


Appendix B.  Revision History

   00 - Initial Revision, split from draft-divilly-atom-hierarchy-01.

   01 - Limited scope of in-lining to Atom.
      Removed type attribute from ae:inline as well as support for non-
      Atom in-lining.
      Specified the interpretation of type attribute and the value of
      ae:inline
      Added example for empty inline element












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Author's Address

   Nikunj R. Mehta
   Oracle Corp.

   Email: nikunj.mehta@oracle.com
   URI:   http://o-micron.blogspot.com/












































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