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Versions: 00 01 02 03 04 05 06                                          
Network Working Group                                           R. Sayre
Internet-Draft                                           October 3, 2005
Expires: April 6, 2006


                  The Atom Publishing Protocol (Basic)
               draft-sayre-atompub-protocol-basic-01.txt

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.
   This document may not be modified, and derivative works of it may not
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   Internet-Drafts are working documents of the Internet Engineering
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   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 6, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This memo presents a protocol for using XML (Extensible Markup
   Language) and HTTP (HyperText Transport Protocol) to edit content.

   The Atom Publishing Protocol is an application-level protocol for
   publishing and editing Web resources belonging to periodically
   updated websites.  The Atom format is documented in the Atom
   Syndication Format (draft-ietf-atompub-format-11.txt).



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Editorial Note

   To provide feedback on this Internet-Draft, join the atom-protocol
   mailing list <http://www.imc.org/atom-protocol/index.html>.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Notational Conventions . . . . . . . . . . . . . . . . . . .   4
   3.   The Atom Publishing Protocol Model . . . . . . . . . . . . .   5
   4.   Collections  . . . . . . . . . . . . . . . . . . . . . . . .   9
   5.   Media Collections  . . . . . . . . . . . . . . . . . . . . .  12
   6.   Service Outlines . . . . . . . . . . . . . . . . . . . . . .  14
   7.   Security Considerations  . . . . . . . . . . . . . . . . . .  16
   8.   Normative References . . . . . . . . . . . . . . . . . . . .  16
        Author's Address . . . . . . . . . . . . . . . . . . . . . .  17
   A.   Contributors . . . . . . . . . . . . . . . . . . . . . . . .  18
        Intellectual Property and Copyright Statements . . . . . . .  19

































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1.  Introduction

   The Atom Publishing Protocol (APP) is an application-level protocol
   for publishing and editing Web resources using HTTP [RFC2616] and XML
   [W3C.REC-xml-20040204].














































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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 [RFC2119].

   The APP namespace is "http://purl.org/atom/app#".  This specification
   refers to it by using the prefix "pub", but that prefix is arbitrary.

   The terms 'URI' and 'IRI' are shorthand for the identifiers specified
   in [RFC3986] and [RFC3987].








































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3.  The Atom Publishing Protocol Model

   The Atom Publishing Protocol operates on collections of Web
   resources.  All collections support the same basic interactions, as
   do the resources within the collections.  The patterns of interaction
   are based on the common HTTP verbs.  This section illustrates the
   editing cycle for Atom entries.

   o  GET is used to retrieve a representation of a resource or perform
      a read-only query.

   o  POST is used to create a new, dynamically-named resource.

   o  PUT is used to update a known resource.

   o  DELETE is used to remove a resource.


3.1  Collections

   The APP groups resources into "Collections", which are analogous to
   the "folders" or "directories" found in many file systems.

3.2  Discovery

   To discover the location of the collections exposed by an APP
   service, the client must locate and request a Service Outline
   (Section 6).  Service Outlines describe the layout of an APP service.

   Client                      Server
   |                                |
   |  1.) GET Outline URI           |
   |------------------------------->|
   |                                |
   |  2.) Service Outline Doc       |
   |<-------------------------------|
   |                                |

   1.  The client sends a GET request to the Service Outline Resource.

   2.  The server responds with a Service Outline Document containing
       the locations of collections provided by the service.  The
       content of this document can vary based on aspects of the client
       request, including, but not limited to, authentication
       credentials.






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3.3  Listing

   Once the client has discovered the location of a collection, it can
   request a listing of the collection's membership.  However,
   collections might be extremely large, so servers are likely to list a
   small subset of the collection by default.

   Client                      Server
   |                                |
   |  1.) GET to Collection URI     |
   |------------------------------->|
   |                                |
   |  2.) 200 OK, Atom Feed Doc     |
   |<-------------------------------|
   |                                |

   1.  The client sends a GET request to the Collection's URI.

   2.  The server responds with an Atom Feed Document containing a full
       or partial listing of the collection's membership.


3.4  Authoring

   After locating a collection, a client can add entries by sending a
   request to the collection; other changes are accomplished by sending
   HTTP requests to its member resources.

3.4.1  Create

   Client                      Server
   |                                |
   |  1.) POST to Collection URI    |
   |------------------------------->|
   |                                |
   |  2.) 201 Created @ Location    |
   |<-------------------------------|
   |                                |

   1.  The client sends a representation of a member to the server via
       HTTP POST.  The Request URI is that of the Collection.

   2.  The server responds with a response of "201 Created" and a
       "Location" header containing the URI of the newly-created
       resource.






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3.4.2  Read

   Client                      Server
   |                                |
   |  1.) GET or HEAD to Member URI |
   |------------------------------->|
   |                                |
   |  2.) 200 OK Atom Entry         |
   |<-------------------------------|
   |                                |


   1.  The client sends a GET (or HEAD) request to the member's URI.

   2.  The server responds with an Atom Entry document.


3.4.3  Update

   Client                      Server
   |                                |
   |  1.) PUT to Member URI         |
   |------------------------------->|
   |                                |
   |  2.) 200 OK                    |
   |<-------------------------------|

   1.  The client PUTs an updated representation to the member's URI.

   2.  The server responds with a representation of the member's new
       state.


3.4.4  Delete

   Client                      Server
   |                                |
   |  1.) DELETE to Member URI      |
   |------------------------------->|
   |                                |
   |  2.) 204 No Content            |
   |<-------------------------------|
   |                                |

   1.  The client sends a DELETE request to the member's URI.

   2.  The server responds with successful status code.




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3.5  Success and Failure

   HTTP defines classes of response.  HTTP status codes of the form 2xx
   signal that a request was successful.  HTTP status codes of the form
   4xx or 5xx signal that an error has occurred, and the request has
   failed.  Consult the HTTP specification for more detailed definitions
   of each status code.












































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4.  Collections

   An Atom Collection is a set of related resources represented by one
   or more Atom Feed documents [AtomFormat].  Atom Collections are
   ordered the date their members were updated, with the most recently
   updated member appearing first.

4.1  GET

   Collections can contain extremely large numbers of resources.  A
   naive client such as a web spider or web browser would be overwhelmed
   if the response to a GET reflected the full membership of the
   collection, and the server would waste large amounts of bandwidth and
   processing time on clients unable to handle the response.  As a
   result, responses to a simple GET request represent a server-
   determined subset of the collection's membership.

   An example collection feed:


   <feed xmlns="http://www.w3.org/2005/Atom"
         xmlns:pub="http://purl.org/atom/app#">
     <title>My Posts1</title>
     <id>urn:uuid:ce61592c-14e2-4557-978e-dfbd444aefa6</id>
     <updated>2005-12-21T04:11:00-08:00</updated>
     <!-- 0 or more atom:entry elements follow -->
     <entry>
      <title type="text">title 25</title>
      <updated>2005-12-21T04:11:00-08:00</updated>
      <author>
        <name>Foo</name>
      </author>
      <id>urn:uuid:941e12b4-6eeb-4753-959d-0cbc51875387</id>
      <pub:edit href="./entry7.atom"/>
      <link href="/permalink7.html" />
     </entry>
     ...
   </feed>


   Each member is represented by an Atom Entry, but those entries are
   not an editable representation of the entry.  To retrieve the source
   representation of the entry, clients send a GET request to the URI
   found in each entry's pub:edit element (see Section 4.3.1).  Derived
   resources are located by examining an entry's atom:link elements.






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4.2  POST

   In addition to GET, a Collection Resource also accepts POST requests.
   The client POSTs a representation of the desired resource to the
   Collection Resource.  Note that some collections only allow members
   of a specific media-type and a POST MAY generate a response with a
   status code of 415 ("Unsupported Media Type").

   In the case of a successful creation, the status code MUST be 201
   ("Created").

   Example request creating a resource in a collection.

   POST /collection HTTP/1.1
   Host: example.org
   User-Agent: Cosimo/1.0
   Content-Type: application/atom+xml
   Content-Length: nnnn

   ...data...

   Example response.

   HTTP/1.1 201 Created
   Date: Mon, 21 Mar 2005 19:20:19 GMT
   Server: CountBasic/2.0
   ETag: "4c083-268-423f1dc6"
   Location: http://example.org/stuff/foo13241234.atom


4.3  Entry Collection

   Entry Collections are Collections that restrict their membership to
   Atom entries.  The entries are edited by sending HTTP requests to the
   URI found in an individual entry's pub:edit element.  Servers can
   determine the processing necessary to interpret a request by
   examining the request's HTTP method.

4.3.1  The 'pub:edit' Element

   The pub:edit element has one attribute, 'href'.  The value of this
   attribute is an IRI reference interpreted relative to xml:base.

4.3.2  Role of Atom Entry Elements During Editing

   The elements of an Atom Entry Document are either a 'Writable
   Element' or a 'Round Trip Element'.




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   Writable Element - An element of an Atom Entry whose value is
   editable by the client and not enforced by the server.

   Round Trip Element - An element of an Atom Entry whose value is
   enforced by the server and not editable by the client.

   That categorization determines the elements' disposition during
   editing.

                  +--------------------+------------+
                  | Atom Entry Element |  Property  |
                  +--------------------+------------+
                  |     atom:author    |  Writable  |
                  |                    |            |
                  |    atom:category   |  Writable  |
                  |                    |            |
                  |    atom:content    |  Writable  |
                  |                    |            |
                  |  atom:contributor  |  Writable  |
                  |                    |            |
                  |       atom:id      | Round Trip |
                  |                    |            |
                  |      atom:link     |  Writable  |
                  |                    |            |
                  |   atom:published   |  Writable  |
                  |                    |            |
                  |     atom:source    |  Writable  |
                  |                    |            |
                  |    atom:summary    |  Writable  |
                  |                    |            |
                  |     atom:title     |  Writable  |
                  |                    |            |
                  |    atom:updated    | Round Trip |
                  +--------------------+------------+

                                  Table 1















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5.  Media Collections

   Media Collections are Collections that do not have uniform
   restrictions on the representations of the member resources.  For
   example, they might contain JPEG images, text documents, MPEG movies,
   and any other type of resource the server allows.

5.1  GET

   Media Collections return an Atom feed much like Entry Collections,
   but with a few additions.  The listing MUST also contain an atom:
   content element with a 'src' attribute pointing to the media
   resource.  This URI can be used to edit the uploaded media resource,
   using PUT and DELETE.

   Such entries MAY contain pub:edit elements used to edit the entry
   metadata.  As with other collection members, derived resources can be
   located by inspecting an entry's atom:link elements.

   An example Media Collection feed:


   <feed xmlns="http://www.w3.org/2005/Atom"
         xmlns:pub="http://purl.org/atom/app#">
     <title>My Posts1</title>
     <author>
       <name>Foo</name>
     </author>
     <id>urn:uuid:ce61592c-14e2-4557-978e-dfbd444aefa6</id>
     <updated>2005-12-21T04:11:00-08:00</updated>
     <!-- 0 or more atom:entry elements follow -->
     <entry>
      <title type="text">title 25</title>
      <updated>2005-12-21T04:11:00-08:00</updated>
      <id>urn:uuid:941e12b4-6eeb-4753-959d-0cbc51875387</id>
      <link href="/permalink7.html" type="text/html" />
      <link href="/stuff/public/beach.jpg" type="image/jpg"
            title="Low res public version" />
      <summary>this was awesome</summary>
      <content src="http://example.org/asdf.jpg" />
     </entry>
     ...
   </feed>


   The Atom Syndication Format requires that each such entry contain an
   atom:title and atom:summary element.  This requirement can be
   challenging to meet without requiring users to enter tedious



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   metadata, but servers SHOULD attempt to provide textual data about
   the resource in the interests of accessibility.  The atom:title
   element will likely be provided by the client, as way for users to
   associate their local resources with those they have uploaded to the
   server (see POST below).

5.2  POST

   To create media resources, clients POST the resource to the Media
   Collection's URI.  Clients SHOULD provide a 'Title' request header to
   provide the server with a short string identifying the resource to
   users.  Clients MAY include a 'Content-Description' header [RFC2045]
   providing a more complete description of the content.  In addition,
   servers MAY inspect the POSTed entity for additional metadata to be
   exposed in an atom:entry when listed in a Media Collection.  For
   example, the server might inspect a JPEG file for EXIF headers
   containing creator data.

   An example request.


   POST /collection HTTP/1.1
   Host: example.org
   User-Agent: Cosimo/1.0
   Content-Type: image/jpg
   Content-Length: nnnn
   Title: A Trip to the beach
   Content-Description: It was so fun.

   ...binary data...


   An example request.


   HTTP/1.1 201 Created
   Date: Mon, 21 Mar 2005 19:20:19 GMT
   Server: CountBasic/2.0
   ETag: "4c083-268-423f1dc6"
   Location: http://example.org/stuff/beach.jpg











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6.  Service Outlines

   In order for authoring to commence, a client must first discover the
   capabilities and locations of collections offered.

   The Service Outline Document is a XOXO outline [XOXO].  The top level
   list items describe distinct groups of resources offered by the
   service.  For example, a user with an account containing three blogs
   would have 3 items at the top of the outline.  There is no
   requirement that servers support multiple top-level items, and a
   collection may appear in more than one location in the document.

   Clients can read entries contained in a collection by visiting an the
   URI located in the 'href' attribute of a XOXO outline item.  This URI
   also serves as the location a client POSTs new entries to.  The 'rel'
   attribute of the XHTML anchor element conveys the nature of a
   collection's member resources.  This specification defines two
   initial values for the 'rel' attribute:

   o  entry

   o  media

   These values correspond to the two types of collection defined by
   this specification.  Extensibility for 'rel' values is specified in
   XHTML Modularization [W3C.REC-xhtml-modularization-20010410].

























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   An example Service Outline:


   <ul class="xoxo">
     <li>
       <a href="/app/collection.py?id=1&amp;type=entries"
          rel="entry" type="application/atom+xml">Main Blog</a>
          <ul>
            <li><a href="/app/collection.py?id=2&amp;type=media"
                   rel="media" type="application/atom+xml">My Stuff2</a>
            </li>
          </ul>
     </li>
     <li>
       <a href="/app/collection.py?id=3&amp;type=entries"
          rel="entry" type="application/atom+xml">Side Bar Blog</a>
          <ul>
            <li><a href="/app/collection.py?id=4&amp;type=media"
                   rel="media" type="application/atom+xml">My Stuff4</a>
            </li>
          </ul>
     </li>
     <li>
        <a href="/app/collection.py?id=5&amp;type=entries"
           rel="entry" type="application/atom+xml">A Third Blog</a>
           <ul>
             <li>
               <a href="/app/collection.py?id=6&amp;type=media"
                  rel="media" type="application/atom+xml">My Stuff6</a>
             </li>
           </ul>
     </li>
   </ul>


















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7.  Security Considerations

   Because APP is a publishing protocol, it is important that only
   authorized users can create and edit entries.

   APP relies on HTTP Authentication.  See [RFC2617] for more detailed
   description of the security properties of HTTP Authentication.

8.  Normative References

   [AtomFormat]
              Nottingham, M. and R. Sayre, "The Atom Syndication
              Format",  work-in-progress, August 2005.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

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

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

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

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [W3C.REC-xhtml-modularization-20010410]
              Altheim, M., Boumphrey, F., McCarron, S., Dooley, S.,
              Schnitzenbaumer, S., and T. Wugofski, "Modularization of
              XHTML", W3C REC REC-xhtml-modularization-20010410,
              April 2001.

   [W3C.REC-xml-20040204]
              Yergeau, F., Paoli, J., Sperberg-McQueen, C., Bray, T.,
              and E. Maler, "Extensible Markup Language (XML) 1.0 (Third
              Edition)", W3C REC REC-xml-20040204, February 2004.




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   [XOXO]     Marks, K., Celik, T., Pilgrim, M., and M. Peterson, "XOXO
              1.0: Extensible Open XHTML Outlines", October 2004.


Author's Address

   Robert Sayre

   Email: rfsayre@boswijck.com
   URI:   http://boswijck.com









































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Appendix A.  Contributors

   This draft is a variant of the in-progress Atom Publishing Protocol
   specification from the IETF Atompub WG, and owes a debt to the WG's
   members.














































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Intellectual Property Statement

   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
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   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.

   The IETF has been notified of intellectual property rights claimed in
   regard to some or all of the specification contained in this
   document.  For more information consult the online list of claimed
   rights.


Disclaimer of Validity

   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 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.


Copyright Statement

   Copyright (C) The Internet Society (2005).  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.





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Acknowledgment

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















































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