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Network Working Group                                           J. Snell
Internet-Draft                                          October 10, 2006
Expires: April 13, 2007


              Atom Publishing Protocol Features Extension
                   draft-snell-atompub-feature-01.txt

Status of this Memo

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   This Internet-Draft will expire on April 13, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document introduces extensions to the Atom Publishing Protocol
   introspection format for expressing metadata about the features
   supported by an Atom Publishing Protocol server implementation.









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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . . . 3
   3.  Feature Introspection and the 'f:feature' element . . . . . . . 3
     3.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Publishing Controls and the 'f:control' element . . . . . . . . 5
     4.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 8
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9





































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1.  Introduction

   This document introduces extensions for the Atom Publishing Protocol
   introspection format for expressing metadata about the features
   supported by an Atom Publishing Protocol server implementation.


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 BCP 14, [RFC2119].

   This specification uses XML Namespaces [W3C.REC-xml-names-19990114]
   to uniquely identify XML element names.  It uses the following
   namespace prefix for the indicated namespace URI;

     "f": "http://purl.org/atompub/features/1.0"

   This specification uses terms from the XML Infoset [W3C.REC-xml-
   infoset-20040204].  However, this specification uses a shorthand; the
   phrase "Information Item" is omitted when naming Element Information
   Items.  Therefore, when this specification uses the terms "element"
   and "attribute" it is referring, respectively, to the Element and
   Attribute Information Items in Infoset terms.


3.  Feature Introspection and the 'f:feature' element

   A feature is an abstract behavior, function and capability supported
   by an Atom Publishing Protocol server.  Examples of features that
   might be supported by an APP server include support for a particular
   set of Atom format extensions, a particular authentication scheme, or
   a specific set of behaviors.  The presence of a f:feature element in
   an app:collection element is an indication that the collection
   supports the feature and may require that a client wishing to use the
   endpoint use that feature.  Features are identified using permanent,
   universally unique IRI's.

     feature = element f:feature {
       atomCommonAttributes,
       attribute ref { atomUri },
       attribute required { 'yes' | 'no' }?,
       attribute href { atomURI }?,
       attribute label { text }?,
       (extensionElement*)
     }




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   The "ref" attribute specifies an IRI that uniquely identifies a
   feature supported by a collection.  The value of the ref attribute
   MUST be compared on a case-sensitive, character-by-character basis.
   Relative references MUST NOT be used.

   A 'required' attribute value of "yes" indicates that clients MUST
   utilize the identified feature when interacting with the collection.
   A server MAY reject requests from clients that do not support or use
   the feature.  If not specified, the value is assumed to be "no".

   An optional 'href' attribute MAY be used to specify the URI of a
   human-readable description of the feature.

   The optional 'label' attribute MAY be used to specify a human-
   readable label for the feature.  The value of the 'label' attribute
   is Language-Sensitive as defined by Section 2 of [RFC4287].

   The f:feature element MAY contain child elements and attributes other
   than those defined in this specification.  Such "foreign markup" are
   considered to be metadata applicable to the feature identified by the
   f:feature element.  Software agents MUST NOT stop processing or
   signal an error or change their behavior as a result of encountering
   such foreign markup.

   An app:collection element MAY contain zero or more f:feature elements
   but MUST NOT contain more than one with the same ref attribute value.
   The order in which f:feature elements appears is insignificant.

3.1.  Example

   The following is an example of a collection supporting one required
   and one optional feature.

     <service xmlns="...">
       <workspace title="My Atom Service">
         <collection title="My Atom Collection" href="...">
           ...
           <f:feature ref="http://example.org/features/changetracking"
             href="http://example.org/features/changetracking.html"
             label="Change Tracking">
             <rh:history xmlns:rh="..." href="revisionhistory.xml" />
           </f:feature>
           <f:feature ref="http://code.google.com/apis/gdata/"
             href="http://code.google.com/apis/gdata/"
             label="Google Data API"
             required="yes" />
         </collection>
       </workspace>



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     </app:server>


4.  Publishing Controls and the 'f:control' element

   Publishing Controls are a mechanism provided by the Atom Publishing
   Protocol to embed metadata within atom:entry elements designed to
   influence the way a server processes the entry.  The pub:control
   element is provided as a convenient container for this metadata
   within an atom:entry.  The Atom Publishing Protocol does not define a
   mechanism by which clients can discover which publishing controls a
   server supports.

   The presence of a f:control element in an app:collection element is
   an indication that the collection supports the control and may
   require that a client wishing to use the endpoint use that control.
   Controls are identified using permanent, universally unique IRI's.

     control = element f:control {
       atomCommonAttributes,
       attribute ref { atomUri },
       attribute required { 'yes' | 'no' }?,
       attribute href { atomURI }?,
       attribute label { text }?,
       (extensionElement*)
     }

   The "ref" attribute specifies an IRI that uniquely identifies a
   control supported by a collection.  The value of the ref attribute
   MUST be compared on a case-sensitive, character-by-character basis.
   Relative references MUST NOT be used.

   A 'required' attribute value of "yes" indicates that clients MUST
   utilize the identified control when interacting with the collection.
   A server MAY reject requests from clients that do not support or use
   the control.  If not specified, the value is assumed to be "no".

   An optional 'href' attribute MAY be used to specify the URI of a
   human-readable description of the control.

   The optional 'label' attribute MAY be used to specify a human-
   readable label for the control.  The value of the 'label' attribute
   is Language-Sensitive as defined by Section 2 of [RFC4287].

   The f:control element MAY contain child elements and attributes other
   than those defined in this specification.  Such "foreign markup" are
   considered to be metadata applicable to the control identified by the
   f:control element.  Software agents MUST NOT stop processing or



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   signal an error or change their behavior as a result of encountering
   such foreign markup.

   An app:collection element MAY contain zero or more f:control elements
   but MUST NOT contain more than one with the same ref attribute value.
   The order in which f:control elements appear is insignificant.

4.1.  Example

   The following is an example of a collection supporting one required
   and one optional control.

     <service xmlns="...">
       <workspace title="My Weblog">
         <collection title="My Entries" href="...">
           ...
           <f:control ref="http://purl.org/atom/app#draft"
                      required="yes" />
           <f:control ref="http://example.org/transforms"
                      required="no">
             <x:transforms xmlns:x="http://example.org/transforms">
               <x:transform>markdown</x:transform>
               <x:transform>wiki</x:transform>
               <x:transform>line-breaks</x:transform>
               <x:none>
             </x:states>
           </f:feature>
         </collection>
       </workspace>
     </app:server>

   An example atom:entry using the listed controls could appear as:

     <entry xmlns="http://www.w3.org/2005/Atom">
       ...
       <control xmlns="...">
         <draft>yes</draft>
         <f:transform>markdown</f:transform>
         <f:transform>line-breaks</f:transform>
       </control>
       ...
     </entry>


5.  Security Considerations

   Specific features and controls supported by a collection may
   introduce security considerations and concerns beyond those discussed



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   by the Atom Publishing Protocol and Atom Syndication Format
   specifications.  Implementors must refer to the specifications and
   description of each feature and control to determine the security
   considerations relevant to each.


6.  IANA Considerations

   This specification does not specify any considerations for IANA.

7.  References

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

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

   [W3C.REC-xml-infoset-20040204]
              Cowan, J. and R. Tobin, "XML Information Set (Second
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-infoset-20040204, February 2004,
              <http://www.w3.org/TR/2004/REC-xml-infoset-20040204>.

   [W3C.REC-xml-names-19990114]
              Layman, A., Bray, T., and D. Hollander, "Namespaces in
              XML", World Wide Web Consortium Recommendation REC-xml-
              names-19990114, January 1999,
              <http://www.w3.org/TR/1999/REC-xml-names-19990114>.


Appendix A.  Acknowledgements

   The author acknowledges the feedback from Elias Torres, Robert Yates,
   David Johnson, Byrne Reese, Joe Gregorio and the other members of the
   IETF Atom Publishing working group during the development of this
   specification.














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Author's Address

   James M Snell


   Phone:
   Email: jasnell@gmail.com
   URI:   http://snellspace.com











































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Intellectual Property Statement

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Copyright Statement

   Copyright (C) The Internet Society (2006).  This document is subject
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   except as set forth therein, the authors retain all their rights.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




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