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Network Working Group                                   J. Gregorio, Ed.
Internet-Draft                                           BitWorking, Inc
Expires: April 14, 2006                                  B. de hOra, Ed.
                                                           Propylon Ltd.
                                                        October 11, 2005


                      The Atom Publishing Protocol
                   draft-ietf-atompub-protocol-05.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.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts.

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   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 14, 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 (APP) is an application-level protocol
   for publishing and editing Web resources.  The protocol at its core
   is the HTTP transport of Atom-formatted representations.  The Atom
   format is documented in the Atom Syndication Format



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   (draft-ietf-atompub-format-11.txt).

Editorial Note

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

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.   XML Namespace and Language . . . . . . . . . . . . . . . . .   5
   3.   Notational Conventions . . . . . . . . . . . . . . . . . . .   6
   4.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.   The Atom Publishing Protocol Model . . . . . . . . . . . . .   8
     5.1  Collections  . . . . . . . . . . . . . . . . . . . . . . .   8
     5.2  Editable Resources . . . . . . . . . . . . . . . . . . . .   9
       5.2.1  Read . . . . . . . . . . . . . . . . . . . . . . . . .  10
       5.2.2  Update . . . . . . . . . . . . . . . . . . . . . . . .  10
       5.2.3  Delete . . . . . . . . . . . . . . . . . . . . . . . .  10
     5.3  Capabilities Discovery . . . . . . . . . . . . . . . . . .  11
     5.4  Listing  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.5  Success and Failure  . . . . . . . . . . . . . . . . . . .  12
   6.   Atom Publishing Protocol Documents . . . . . . . . . . . . .  13
     6.1  Use of xml:base xml:lang . . . . . . . . . . . . . . . . .  13
     6.2  Collection Documents . . . . . . . . . . . . . . . . . . .  14
       6.2.1  Element Definitions  . . . . . . . . . . . . . . . . .  14
     6.3  Introspection Documents  . . . . . . . . . . . . . . . . .  16
       6.3.1  Element Definitions  . . . . . . . . . . . . . . . . .  17
   7.   Introspection Resource . . . . . . . . . . . . . . . . . . .  20
     7.1  Discovery  . . . . . . . . . . . . . . . . . . . . . . . .  20
   8.   Collection Resources . . . . . . . . . . . . . . . . . . . .  21
     8.1  GET  . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
     8.2  POST . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
     8.3  Title: Header  . . . . . . . . . . . . . . . . . . . . . .  22
   9.   Entry Collections  . . . . . . . . . . . . . . . . . . . . .  23
     9.1  Editing Entry Resources  . . . . . . . . . . . . . . . . .  23
     9.2  Role of Atom Entry Elements During Editing . . . . . . . .  23
   10.  Generic Collections  . . . . . . . . . . . . . . . . . . . .  25
     10.1   Editing Generic Resources  . . . . . . . . . . . . . . .  25
     10.2   Title: Header  . . . . . . . . . . . . . . . . . . . . .  25
   11.  List Resources . . . . . . . . . . . . . . . . . . . . . . .  26
     11.1   URI Templates  . . . . . . . . . . . . . . . . . . . . .  26
     11.2   URI Template Parameters  . . . . . . . . . . . . . . . .  27
       11.2.1   \{index\} URI template variable  . . . . . . . . . .  27
       11.2.2   \{daterange\} URI template variable  . . . . . . . .  27
       11.2.3   Other URI Template parameters  . . . . . . . . . . .  28
   12.  Atom Entry Extensions  . . . . . . . . . . . . . . . . . . .  29
   13.  Securing the Atom Protocol . . . . . . . . . . . . . . . . .  30



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   14.  Security Considerations  . . . . . . . . . . . . . . . . . .  31
   15.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  32
   16.  References . . . . . . . . . . . . . . . . . . . . . . . . .  35
     16.1   Normative References . . . . . . . . . . . . . . . . . .  35
     16.2   Informative References . . . . . . . . . . . . . . . . .  36
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  37
   A.   Contributors . . . . . . . . . . . . . . . . . . . . . . . .  38
   B.   Revision History . . . . . . . . . . . . . . . . . . . . . .  39
        Intellectual Property and Copyright Statements . . . . . . .  41










































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1.  Introduction

   The Atom Publishing Protocol is an application-level protocol for
   publishing and editing Web resources using HTTP [RFC2616] and XML 1.0
   [W3C.REC-xml-20040204].














































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2.  XML Namespace and Language

   The XML Namespaces URI [W3C.REC-xml-names-19990114] for the XML data
   format described in this specification is: http://purl.org/atom/app#

   XML elements defined by this specification MAY have an xml:lang
   attribute, whose content indicates the natural language for the
   element (and its descendents).  The language context is only
   significant for elements and attributes declared to be "Language-
   Sensitive" by this specification.  Requirements regarding the content
   and interpretation of xml:lang are specified in [W3C.REC-xml-
   20040204], Section 2.12.







































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3.  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].

   Some sections of this specification are illustrated with fragments of
   a non-normative RELAX NG Compact schema [RNC].  However, the text of
   this specification provides the definition of conformance.

   This specification uses the namespace prefix "app:" for the Namespace
   URI identified in Section 2 above.  It uses the namespace prefix
   "atom:" for the Namespace URI identified in [AtomFormat].  Note that
   choices of namespace prefix are arbitrary and not semantically
   significant.




































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4.  Terminology

   For convenience, this protocol may be referred to as "Atom Protocol"
   or "APP".  This specification uses both internally.

   URI/IRI - A Uniform Resource Identifier and Internationalized
   Resource Identifier, respectively.  These terms (and the distinction
   between them) are defined in [RFC3986] and [RFC3987].

   Resource -  A network data object or service that can be identified
   by a URI, as defined in [RFC2616].

   Representation -  An entity included with a request or response as
   defined in [RFC2616].





































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5.  The Atom Publishing Protocol Model

   The Atom Publishing Protocol is a subset of HTTP that is used to edit
   resources on the web.  The APP operates on collections of Web
   resources.  Collections are HTTP resources, as are the members of the
   collection.  Both Collections and collection member resources support
   the same basic interactions.  The patterns of interaction are based
   on the common HTTP verbs.

   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, or to
      provide a block of data to a data-handling process.

   o  PUT is used to update a known resource.

   o  DELETE is used to remove a resource.


5.1  Collections

   The APP groups resources into "Collections", which are analogous to
   folders or directories found in a file system.  In the figure we have
   member resources in a collection.

          +-------------------------+
          | Collection              |
          |                         |
          |  +----------------+     |
          |  | Member_A       |     |
          |  +----------------+     |
          |                         |
          |  +----------------+     |
          |  | Member_B       |     |
          |  +----------------+     |
          |                         |
          |  +----------------+     |
          |  | Member_C       |     |
          |  +----------------+     |
          |                         |
          |  ...                    |
          |                         |
          |  +----------------+     |
          |  | Member_Oldest  |     |
          |  +----------------+     |
          |                         |
          +-------------------------+



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   To add a new member to a collection an appropriate representation is
   POSTed to the URI of the collection resource.  Here we show it being
   added to the beginnng of the list.  The ordering of the members of
   collections is in terms of the time at which each resource was last
   updated, which includes the act of creating the resource.  The
   ordering of collection members is covered in more detail in Section 8
   and Section 11.

          +-------------------------+
          | Collection              |
          |                         |
    POST  |  +----------------+     |
   --------->| Member_New     |     |
          |  +----------------+     |
          |                         |
          |  +----------------+     |
          |  | Member_A       |     |
          |  +----------------+     |
          |                         |
          |  +----------------+     |
          |  | Member_B       |     |
          |  +----------------+     |
          |                         |
          |  +----------------+     |
          |  | Member_C       |     |
          |  +----------------+     |
          |                         |
          |  ...                    |
          |                         |
          |  +----------------+     |
          |  | Member_Oldest  |     |
          |  +----------------+     |
          |                         |
          +-------------------------+

   You'll note that up until now we haven't said what kinds of
   representations we are expecting at each of the resources.  There are
   two kinds of collections, Entry and Generic.  In Entry Collections
   all the members MUST have representations as Atom Entries.  For
   further restrictions on Entry Collection see Section 9 The other type
   of collection is a Generic Collection.  Generic Collections make no
   restriction on the representations of their member resources.

5.2  Editable Resources

   All the members of a collection are Editable Resources.  An Editable
   resource is a resource whose available HTTP methods can be used to
   retrieve, update and delete it.



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5.2.1  Read

   To retrieve a representation of the resource, you send a GET to the
   URI of the Editable Resource.  Remember that for members of Entry
   Collections, the served representation will be an Atom Entry.

   Client                                   Server
     |                                           |
     |  1.) GET to Editable Resource URI         |
     |------------------------------------------>|
     |                                           |
     |  2.) 200 OK                               |
     |<------------------------------------------|
     |                                           |

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

   2.  The server responds with the representation of the resource.


5.2.2  Update

   To update an Editable Resource the client will PUT an updated
   representation to the URI of the resource.

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

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

   2.  The server MAY respond with an updated representation of the
       member's new state.


5.2.3  Delete

   An Editable Resource is deleted by sending it DELETE.  Note that this
   also removes it from all the collections that it belonged to.








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   Client                                     Server
     |                                           |
     |  1.) DELETE to Editable Resource URI      |
     |------------------------------------------>|
     |                                           |
     |  2.) 200 Ok                               |
     |<------------------------------------------|
     |                                           |

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

   2.  The server responds with successful status code.


5.3  Capabilities Discovery

   Each collection resource responds to GET and can return a Collection
   Document as it's representation.  The Collection Document enumerates
   the capabilities of each collection and the format is described in
   Section 6.2.

   Client                         Server
     |                                |
     |  1.) GET to Collection         |
     |------------------------------->|
     |                                |
     |  2.) Collection Document       |
     |<-------------------------------|
     |                                |

   1.  The client sends a GET request to the Collection Resource.

   2.  The server responds with a Collection Document containing a
       description of the capabilities of the collection.  The content
       of this document can vary based on aspects of the client request,
       including, but not limited to, authentication credentials.


5.4  Listing

   Clients can request a listing of the Collection's membership.
   Listing the Editable Resources that are members of a collection is
   done using one of the List Resources in the Introspection Document,
   utilizing the 'app:uri-template' element.  The List Resource returns
   Atom Feed Documents with one Atom Entry for each member resource that
   match the selection criteria.  This is true whether the collection is
   an Entry Collection or a Generic Collection.  If an Entry Collection
   is being interrogated, the entries returned by a list resource SHOULD



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   NOT to be considered complete representations of the member
   resources.  See Section 11 and Section 12 for more details on the
   extensions and constraints found on the entries returned from List
   Resources.

   Client                          Server
     |                                |
     |  1.) GET to List Resource      |
     |------------------------------->|
     |                                |
     |  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.


5.5  Success and Failure

   HTTP defines different classes of response, which are used by the
   Atom Protocol.  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 [RFC2616] for more detailed
   definitions of each status code.























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6.  Atom Publishing Protocol Documents

   This specification describes two kinds of Atom Publishing Protocol
   Documents: Atom Collections Documents and Atom Introspection
   Documents.

   An Atom Collection Document is a representation of an Atom
   collection, including metadata about the collection, and some or all
   of the members associated with it.  Its root is the app:collection
   element.

   An Atom Introspection Document represents one or more workspaces,
   which describe server-defined groupings of collections.  Its root is
   the app:service element.

   namespace app = "..." start = appCollection | appIntrospection

   Both kinds of Atom Publishing Protocol Documents are specified in
   terms of the XML Information Set, serialised as XML 1.0 ([W3C.REC-
   xml-20040204]).  Atom Publishing Protocol Documents MUST be well-
   formed XML.  This specification does not define a DTD for Atom
   Protocol, and hence does not require them to be valid (in the sense
   used by XML).

   Atom Collection Documents are identified with the "application/
   atomcoll+xml" media type.

   Atom Introspection Documents are identified with the "application/
   atomserv+xml" media type.

   Atom allows the use of IRIs [RFC3987], as well as URIs [RFC3986].
   Every URI is an IRI, so any URI can be used where an IRI is needed.
   While IRIs must, for many protocols, be mapped to URIs prior to
   dereferencing, they MUST NOT be so mapped for comparison when used in
   atom:id.  Section 3.1 of [RFC3987] describes how to map an IRI to a
   URI when necessary.

6.1  Use of xml:base xml:lang

   Any element defined by this specification MAY have an xml:base
   attribute [W3C.REC-xmlbase-20010627].  When xml:base is used in an
   Atom Publishing Protocol Document, it serves the function described
   in section 5.1.1 of [RFC3986], establishing the base URI (or IRI) for
   resolving any relative references found within the effective scope of
   the xml:base attribute.

   Any element defined by this specification MAY have an xml:lang
   attribute, whose content indicates the natural language for the



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   element and its descendents.  The language context is only
   significant for elements and attributes declared to be "Language-
   Sensitive" by this specification.  Requirements regarding the content
   and interpretation of xml:lang are specified in XML 1.0 ([W3C.REC-
   xml-20040204]), Section 2.12.

    appCommonAttributes =
         attribute xml:base { atomUri }?,
         attribute xml:lang { atomLanguageTag }?,
        undefinedAttribute*


6.2  Collection Documents

   The Collection Document describes the capabilities of a Collection,
   the types of Entries that it will support, the URI Templates it
   supports.

   The Collection Document has the media-type 'application/atomcoll+xml'
   (see Section 15).

   Here's an example document:

   <?xml version="1.0" encoding='utf-8'?>
   <app:collection xmlns:app="http://purl.org/atom/app#">
     <app:member-type>entry</pub:member-type>
     <app:uri-template>http://example.org/{index}</pub:uri-template>
     <app:uri-template>http://example.org/{daterange}</pub:uri-template>
   </app:collection>

   This example says the Collection contains Atom Entry documents, and
   that there are two means of selecting entries using what are called
   'URI Templates'; one based on the collection's order, and another
   based on dates.  See Section 11.1 for more about URI Templates.

6.2.1  Element Definitions

6.2.1.1  The 'app:collection' Element

   The app:collection is the document element of a Collection Document.


   appCollection =
      element app:collection {
         appCommonAttributes,
         ( appMemberType+
           appSearchTemplate
           & anyElement* )



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      }


   This specification defines two child elements for app:collection:

   o  app:member-type: any number of elements listing the types of
      Entries that the Collection may contain.

   o  app:uri-template: any number of URI Templates for a List Resource
      (See Section 11).


6.2.1.2  The 'app:member-type' Element

   The app:member-type element contains information elements about the
   types of Entries that the Collection may contain.


   appMember =
      element app:member-type {
            appCommonAttributes,
            appTypeValue
      }


   The element content of an app:member-type MUST be a string that is
   non-empty, and matches either the "isegment-nz-nc" or the "IRI"
   production in [RFC3987].  Note that use of a relative reference other
   than a simple name is not allowed.  If a name is given,
   implementations MUST consider the link relation type to be equivalent
   to the same name registered within the IANA Registry of Member Types
   (Section 15), and thus the IRI that would be obtained by appending
   the value of the rel attribute to the string
   "http://www.iana.org/assignments/entrytype/".

   The content of an app:member-type specifies constraints on the
   Entries that may appear in the Collection.  The app:collection
   element MAY have multiple app:member-type elements.  An Entry POSTed
   to a Collection MUST meet the constraints of at least one of the app:
   member-type constraints.  It MAY meet more than one, but the minimum
   requirement is at least one.

   This specification defines two initial values for app:member-type
   IANA registry:

   o  "entry" - The Collection is an Entry Collection as defined in
      Section 9.




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   o  "generic" - The Collection is a Generic Collection as defined in
      Section 10.


6.2.1.3  The 'app:uri-template' Element

   The element content of an app:uri-template is a URI Template for a
   List Resource (See Section 11).  Every List resource, whose URI is
   determined by filling in the parameters in a URI Template, MUST
   return an Atom feed document as its representation.  This Atom feed
   document MUST NOT contain entries which do not match the selection
   criteria.

6.3  Introspection Documents

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

   The Introspection Document describes "workspaces", which are server-
   defined groupings of collections.  There is no requirement that
   servers support multiple workspaces, and a collection may appear in
   more than one workspace.

   The Introspection Document has the media-type 'application/
   atomserv+xml', see Section 15

   Here's an example document:

   <?xml version="1.0" encoding='utf-8'?>
   <app:service xmlns:app="http://purl.org/atom/app#">
     <app:workspace title="Main Site" >
         <app:collection contents="entries"
             title="My Blog Entries"
             href="http://example.org/reilly/feed" />
         <app:collection contents="generic"
             title="Documents"
             href="http://example.org/reilly/pic" />
     </app:workspace>
     <app:workspace title="Side Bar Blog">
         <app:collection contents="entries" title="Entries"
             href="http://example.org/reilly/feed" />
         <app:collection contents="http://example.net/booklist"
             title="Books"
             href="http://example.org/reilly/books" />
     </app:workspace>
   </app:service>

   This example says there are two workspaces, each consisting of two



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   collections.  The first workspace is called 'Mail', and has two
   collections, called 'My Blog Entries' and 'Documents' whose locations
   are 'http://example.org/reilly/feed' and
   'http://example.org/reilly/pic'.  'My Blog Entries' contains Atom
   Entries and 'Documents' contains Generic Entries.  The second
   workspace is called 'Side Bar Blog' and also has two collections,
   called 'Entries' and 'Books' whose locations are
   'http://example.org/reilly/feed' and
   'http://example.org/reilly/booklist'.  'Entries' contains Atom
   Entries and 'Books' contains Generic Entries (since its contents
   attribute is not present you MUST assume it is a Generic Collection).

6.3.1  Element Definitions

6.3.1.1  The 'app:service' Element

   The "app:service" element is the document element of a Introspection
   Document, acting as a container for service data associated with one
   or more workspaces.  An app:service elements MAY contain any number
   of app:workspace elements.


   appService =
      element app:service {
         appCommonAttributes,
         ( appWorkspace*
           & anyElement* )
      }


6.3.1.2  The 'app:workspace' Element

   The 'workspace' element contains information elements about the
   collections of resources available for editing.  The app:workspace
   elements MAY contain any number of app:collection elements.


   appWorkspace =
      element app:workspace {
         appCommonAttributes,
         attribute title { text },
         ( appCollection*
           & anyElement* )
      }







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6.3.1.2.1  The 'title' Attribute

   The app:workspace element MUST contain a 'title' attribute, which
   conveys a human-readable name for the workspace.  This attribute is
   Language-Sensitive.

6.3.1.3  The 'app:collection' Element

   The 'app:collection' element describes collections and their member
   resources.


   appCollection =
      element app:collection {
         appCommonAttributes,
         attribute title { text },
         attribute href { text },
         attribute contents { text },
         anyElement*
      }


6.3.1.3.1  The 'title' Attribute

   The app:collection element MUST contain a 'title' attribute, whose
   value conveys a human-readable name for the workspace.  This
   attribute is Language-Sensitive.

6.3.1.3.2  The 'href' Attribute

   The app:collection element MUST contain an 'href' attribute, whose
   value conveys the IRI of the collection.

6.3.1.3.3  The 'contents' Attribute

   The app:collection element MAY contain a 'contents' attribute.  The
   'contents' attribute conveys the nature of a collection's member
   resources.  This specification defines two initial values for the
   'contents' attribute:

   o  'entry': A value of 'entry' for the contents attribute indicates
      that the Collection is an Entry Collection (Section 9).

   o  'generic': A value of 'generic' for the contents attribute
      indicates that the Collection is a Generic Collection
      (Section 10).

   If the attribute is not present, its value MUST be considered to be



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   'generic'.


















































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7.  Introspection Resource

   To retrieve an Introspection Document, the client sends a GET request
   to its URI.

   GET /service-desc HTTP/1.1
   Host: example.org
   User-Agent: Cosimo/1.0
   Accept: application/atomserv+xml

   The server responds to a GET request by returning an Introspection
   Document in the message body.

   HTTP/1.1 200 OK
   Date: Mon, 21 Mar 2005 19:20:19 GMT
   Server: CountBasic/2.0
   Last-Modified: Mon, 21 Mar 2005 19:17:26 GMT
   ETag: "4c083-268-423f1dc6"
   Content-Length: nnnn
   Content-Type: application/atomserv+xml

   <?xml version="1.0" encoding='utf-8'?>
   <app:service xmlns:app="http://purl.org/atom/app#">
       ...
   </app:service>


7.1  Discovery

   [[anchor18: Add in desc of an HTML link element that points to the
   Introspection Resource, or add it to the autodisco draft]]




















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8.  Collection Resources

   An Atom Collection is a set of related resources.  All members of a
   collection have an "app:updated" property, and the Collection is
   considered to be ordered by this property.

   This specification defines two HTTP methods for use with collection
   resources: GET and POST.

8.1  GET

   A GET to a Collection Resource returns a Collection Document,
   outlining the Collection.  Collection Documents are described in
   Section 6.2.

8.2  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 may impose
   constraints on the media-types that are created in a Collection and
   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").

   Every successful POST MUST return a Location: header with the URI of
   the newly created resource.

   Here's an example.  Below, the client requests to create a resource
   in a Collection:



















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   POST /edit HTTP/1.1
   Host: example.org
   User-Agent: Cosimo/1.0
   Accept: application/atom+xml
   Content-Type: application/atom+xml
   Content-Length: 601

   <atom:entry xmlns:atom="http://www.w3.org/2005/Atom">
     <atom:title>Mars Attacks!</atom:title>
     <atom:summary type="html">
       Why cant we all just... get along?
     </atom:summary>
     <atom:author>
       <atom:name>The President</atom:name>
       <atom:uri>http://www.example.org/blog</atom:uri>
     </atom:author>
     <atom:content type="html" xml:lang="en"
         xml:base="http://www.example.org/blog/">
       <p>
       Why can't we...work out our differences?
       Why can't we...work things out?
       Little people...why can't we all just...get along?
       </p>
     </atom:content>
   </atom:entry>

   The resource is created by sending an Atom Entry as the entity body.

   Assuming the server created the resource successfully, it sends back
   a 201 Created response with a Location: header that contains the IRI
   of the newly created member as an Editable Resource.

   HTTP/1.1 201 Created
   Date: Fri, 7 Oct 2005 17:17:11 GMT
   Content-Length: 663
   Content-Type: application/atom+xml; charset="utf-8"
   Location: http://example.org/edit/first-post.atom



8.3  Title: Header

   The POST to a Collection Resource MAY contain a Title: header that
   indicates the clients suggested name for the resource.  The server
   MAY ignore the Title: header or modify the requested name to suit
   local conventions.

        Title     = "Title" ":" [text]



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9.  Entry Collections

   Entry Collections are Collections that restrict their membership to
   Atom entries.

9.1  Editing Entry Resources

   Atom entries are edited by sending HTTP requests to an individual
   entry's URI.  Servers can determine the processing necessary to
   interpret a request by examining the request's HTTP method and
   'Content-Type' header.

   Processing Client Requests

             +-----------+------+--------+--------+------+
             |           |  GET |   PUT  | DELETE | POST |
             +-----------+------+--------+--------+------+
             |   No Body | Read |    x   | Delete |   x  |
             |           |      |        |        |      |
             | Atom Body |   x  | Update |    x   |   x  |
             +-----------+------+--------+--------+------+


9.2  Role of Atom Entry Elements During Editing

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

   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 will determine the elements' disposition during
   editing.















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                  +--------------------+------------+
                  | 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 2
























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10.  Generic Collections

   Generic Collections are Collections that do not have uniform
   restrictions on the representations of the member resources.

10.1  Editing Generic Resources

   Member resources are edited by sending HTTP requests to an individual
   resource's URI.  Servers can determine the processing necessary to
   interpret a request by examining the request's HTTP method and
   'Content-Type' header.

   Processing Client Requests

              +----------+------+--------+--------+------+
              |          |  GET |   PUT  | DELETE | POST |
              +----------+------+--------+--------+------+
              |  No Body | Read |    x   | Delete |   x  |
              |          |      |        |        |      |
              | Any Body |   x  | Update |    x   |   x  |
              +----------+------+--------+--------+------+

   When a List resource returns an Atom Feed enumerating the contents of
   a Generic Collection, all the Entries MUST have an atom:content
   element with a 'src' attribute.

10.2  Title: Header

   The POST to a Generic Collection Resource MAY contain a Title: header
   that indicates the clients suggested title for the resource.  The
   server MAY ignore the Title: header or modify the requested title to
   suit local conventions.

   Title     = "Title" ":" [text]

















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11.  List Resources

   List resources are resources which are identified by URI templates
   indicating selection criteria.  They can be used where clients
   require fine control over the range or size of a server's response.
   A list resource MUST return an Atom feed document as its
   representation.  The entries in the returned document MUST be ordered
   by their 'atom:updated' property, with the most recently updated
   entries coming first in the document order.  Clients MUST NOT assume
   that the entry returned in the feed is a full representation of a
   member resource.  If the entry is an Editable Resource then the
   client should perform a GET on the member resource before editing.

   note: in this section some URIs carry across onto the next line; this
   is indicated by a '\'

11.1  URI Templates

   URI Templates are a mechanism for declaring criteria against a list
   resource.  By itself a URI Template is not a valid URI.  Instead
   there are multiple parameters embedded in the URI and distinguished
   by closing braces which can be populated and used as selection
   criteria.  The value of each app:uri-template element in a Collection
   document is a URI Template.

   Each URI template has one or more parameters that MUST be substituted
   with values to construct a valid URI.  The substitution MUST ensure
   that the resulting value is also properly percent-encoded utf-8.

   Here are some examples of template URIs and corresponding populated
   values:

   http://example.org/blog/edit/{index}
   http://example.org/blog/edit/3-9

   http://example.org/blog/edit/{index}/foo
   http://example.org/blog/edit/0-100/foo

   http://example.org/blog/edit/{daterange}
   http://example.org/blog/edit/daterange=\
       2003-12-13T18:30:02Z-2003-12-13T18:30:02Z

   http://example.org/blog/edit?dr={daterange}/bar/
   http://example.org/blog/edit?dr=\
       2003-12-13T18:30:02Z,2003-12-13T18:30:02Z/bar/

   Note that the parameters MAY appear at any place in the URI template.




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11.2  URI Template Parameters

   This specification defines two parameters for use in URI Templates:

   o  index: allows selection into a collection's resources based as
      though ordered by their 'atom:updated' property.

   o  daterange: allows selection into a collection's resources based on
      their 'atom:updated' property

   In both cases, the response to the selection request MUST be an Atom
   Feed where all the entries fall within the requested criteria.  The
   request range is considered a closed set - if an entry matches one
   end of the range exactly it MUST be included in the response.  If no
   members fall in the requested range, the server MUST respond with an
   Atom Feed containing no entries.

   A Collection Document MUST contain at least two app:uri-template
   elements - one for the {index} parameter template and the other for
   the {daterange} parameter template.  The two parameters are not
   mutually exclusive and MAY appear together in a single Template URI.

11.2.1  \{index\} URI template variable

   The value of the {index} criterion MUST be a pair of non-negative
   integer indices separated by a dash character.  One or other index
   MAY omitted, in which case the range is understood as stretching to
   zero, or infinity.

    index-specifier = [index] "-" [index]

   For example, suppose the client is supplied this {index} URI
   template:

    http://example.org/blog/edit/{index}

   If the client wants the first 15 entries in the Collection it would
   substitute the brace-delimited parameter {index}, with the value
   1-15, giving:

    http://example.org/blog/edit/1-15


11.2.2  \{daterange\} URI template variable

   A URI Template with the variable 'daterange' allows querying for Atom
   Entries in a Collection according to their 'atom:updated' property.




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   The value of the {daterange} criterion should be a pair of ISO
   formatted dates separated by a dash character; either index may be
   optionally omitted, in which case the range is understood as
   stretching to infinity on that end.

    daterange-specifier = [iso-date] "," [iso-date]

   The [iso-date] terminal MUST conform to the "date-time" production in
   [RFC3339].  In addition, an uppercase "T" character MUST be used to
   separate date and time, and an uppercase "Z" character MUST be
   present in the absence of a numeric time zone offset.

   For example, suppose the client is supplied this {daterange} URI
   Template:

    http://example.org/blog/edit/{daterange}

   If the client wants the entries in the collection between January and
   February 2006 it would substitute the brace-delimited parameter
   {daterange} with the desired selection value, giving this URI:

    http://example.org/blog/edit/2006-01-01T00:00:00Z,\
        2006-02-01T00:00:00Z


11.2.3  Other URI Template parameters

   Other specifications MAY define new parameters for use in URI
   templates and declared in the app:uri-template element.






















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12.  Atom Entry Extensions

   This specification adds three new values to the Registry of Link
   Relations.

   The value of 'collection' signifies that the IRI in the value of the
   href is the Collection that this Entry belongs to.  Any entry MAY
   contain a link with a relation of 'collection'.

   The value of 'edit' signifies that the IRI in the value of the href
   attribute identifies the resource that is used to edit the entry.
   That is, it is the URI of the Entry as an Editable Resource.

   The value of 'srcedit' signifies that the IRI in the value of the
   href attribute identifies the resource that is used to edit the
   resource pointed to by the 'src' attribute of the atom:content
   element.  That is, it is the IRI of the atom:content@src as an
   Editable Resource.  If a link element with a relation of "srcedit" is
   not given, then it's value defaults to the "src" attribute of the
   content element.  List Resources for Generic Collections MUST return
   entries that have 'srcedit' links or MUST have a atom:content@src
   value.

   If the "srcedit" link is present, and it's value is an empty string,
   then there is no URI that can be treated in the way such a value
   would be treated.

   Clients SHOULD use the "srcedit" value to manipulate the resource
   within the context of the APP itself.  Clients SHOULD prefer the
   "atom:content@src" value in any other context.  For example, if the
   resource is an image, a client may replace the image data using a PUT
   on the "srcedit" value, and may even display a preview of the image
   by fetching the "srcedit" URI.  But when creating a public, read-only
   reference to the same image resource, the client should use the
   "atom:content@src" value.
















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13.  Securing the Atom Protocol

   All instances of publishing Atom entries SHOULD be protected by
   authentication to prevent posting or editing by unknown sources.
   Atom servers and clients MUST support one of the following
   authentication mechanisms, and SHOULD support both.

   o  HTTP Digest Authentication [RFC2617]

   o  [@@TBD@@ CGI Authentication ref]

   Atom servers and clients MAY support encryption of the Atom session
   using TLS [RFC2246].

   There are cases where an authentication mechanism may not be
   required, such as a publicly editable Wiki, or when using the PostURI
   to post comments to a site that does not require authentication to
   create comments.

13.1  [@@TBD@@ CGI Authentication]

   This authentication method is included as part of the protocol to
   allow Atom servers and clients that cannot use HTTP Digest
   Authentication but where the user can both insert its own HTTP
   headers and create a CGI program to authenticate entries to the
   server.  This scenario is common in environments where the user
   cannot control what services the server employs, but the user can
   write their own HTTP services.























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14.  Security Considerations

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

   The security of Atom is based on HTTP Digest Authentication and/or
   [@@TBD@@ CGI Authentication].  Any weaknesses in either of these
   authentication schemes will affect the security of the Atom
   Publishing Protocol.

   Both HTTP Digest Authentication and [@@TBD@@ CGI Authentication] are
   susceptible to dictionary-based attacks on the shared secret.  If the
   shared secret is a password (instead of a random string with
   sufficient entropy), an attacker can determine the secret by
   exhaustively comparing the authenticating string with hashed results
   of the public string and dictionary entries.

   See RFC 2617 for more detailed description of the security properties
   of HTTP Digest Authentication.

   @@TBD@@ Talk here about using HTTP basic and digest authentication.

   @@TBD@@ Talk here about denial of service attacks using large XML
   files, or the billion laughs DTD attack.



























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15.  IANA Considerations

   A Atom Collection Document, when serialized as XML 1.0, can be
   identified with the following media type:

   MIME media type name: application

   MIME subtype name: atomcoll+xml

   Mandatory parameters: None.

   Optional parameters:

      "charset": This parameter has identical semantics to the charset
         parameter of the "application/xml" media type as specified in
         [RFC3023].

   Encoding considerations: Identical to those of "application/xml" as
      described in [RFC3023], section 3.2.

   Security considerations: As defined in this specification.
      [[anchor31: update upon publication]]

      In addition, as this media type uses the "+xml" convention, it
      shares the same security considerations as described in [RFC3023],
      section 10.

   Interoperability considerations: There are no known interoperability
      issues.

   Published specification: This specification. [[anchor32: update upon
      publication]]

   Applications that use this media type: No known applications
      currently use this media type.

   Additional information:

   Magic number(s): As specified for "application/xml" in [RFC3023],
      section 3.2.

   File extension: .atomcoll

   Fragment identifiers: As specified for "application/xml" in
      [RFC3023], section 5.






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   Base URI: As specified in [RFC3023], section 6.

   Macintosh File Type code: TEXT

   Person and email address to contact for further information: Joe
      Gregorio <joe@bitworking.org>

   Intended usage: COMMON

   Author/Change controller: IESG

   An Atom Introspection Document, when serialized as XML 1.0, can be
   identified with the following media type:

   MIME media type name: application

   MIME subtype name: atomserv+xml

   Mandatory parameters: None.

   Optional parameters:

      "charset": This parameter has identical semantics to the charset
         parameter of the "application/xml" media type as specified in
         [RFC3023].

   Encoding considerations: Identical to those of "application/xml" as
      described in [RFC3023], section 3.2.

   Security considerations: As defined in this specification.
      [[anchor33: update upon publication]]

      In addition, as this media type uses the "+xml" convention, it
      shares the same security considerations as described in [RFC3023],
      section 10.

   Interoperability considerations: There are no known interoperability
      issues.

   Published specification: This specification. [[anchor34: update upon
      publication]]

   Applications that use this media type: No known applications
      currently use this media type.

   Additional information:





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   Magic number(s): As specified for "application/xml" in [RFC3023],
      section 3.2.

   File extension: .atomsrv

   Fragment identifiers: As specified for "application/xml" in
      [RFC3023], section 5.

   Base URI: As specified in [RFC3023], section 6.

   Macintosh File Type code: TEXT

   Person and email address to contact for further information: Joe
      Gregorio <joe@bitworking.org>

   Intended usage: COMMON

   Author/Change controller: This specification's author(s). [[anchor35:
      update upon publication]]
































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16.  References

16.1  Normative References

   [AtomFormat]
              Nottingham, M. and R. Sayre, "The Atom Syndication
              Format",  1.0, July 2005.

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

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

   [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.

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

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, July 2002.

   [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-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.

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







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16.2  Informative References

   [RNC]      Clark, J., "RELAX NG Compact Syntax", December 2001.

   [W3C.REC-webarch-20041215]
              Walsh, N. and I. Jacobs, "Architecture of the World Wide
              Web, Volume One", W3C REC REC-webarch-20041215,
              December 2004.











































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URIs

   [1]  <http://www.imc.org/atom-protocol/index.html>


Authors' Addresses

   Joe Gregorio (editor)
   BitWorking, Inc
   1002 Heathwood Dairy Rd.
   Apex, NC  27502
   US

   Phone: +1 919 272 3764
   Email: joe@bitworking.com
   URI:   http://bitworking.com/


   Bill de hOra (editor)
   Propylon Ltd.
   45 Blackbourne Square, Rathfarnham Gate
   Dublin, Dublin  D14
   IE

   Phone: +353-1-4927444
   Email: bill.dehora@propylon.com
   URI:   http://www.propylon.com/
























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Appendix A.  Contributors

   The content and concepts within are a product of the Atom community
   and the Atompub Working Group.  Robert Sayre was an editor for drafts
   00-04.














































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Appendix B.  Revision History

   draft-ietf-atompub-protocol-05 - Added: Contributors section.  Added:
   de hOra to editors.  Fixed: typos.  Added diagrams and description to
   model section.  Incorporates PaceAppDocuments, PaceAppDocuments2,
   PaceSimplifyCollections2 (large-sized chunks of it anyhow: the
   notions of Entry and Generic resources, the section 4 language on the
   Protocol Model, 4.1 through 4.5.2, the notion of a Collection
   document, as in Section 5 through 5.3, Section 7 "Collection
   resources", Selection resources (modified from pace which talked
   about search); results in major mods to Collection Documents, Section
   9.2 "Title: Header" and brokeout para to section 9.1 Editing Generic
   Resources).  Added XML namespace and language section.  Some cleanup
   of front matter.  Added Language Sensitivity to some attributes.
   Removed resource descriptions from terminology.  Some juggling of
   sections.  See:
   http://www.imc.org/atom-protocol/mail-archive/msg01812.html.

   draft-ietf-atompub-protocol-04 - Add ladder diagrams, reorganize, add
   SOAP interactions

   draft-ietf-atompub-protocol-03 - Incorporates PaceSliceAndDice3 and
   PaceIntrospection.

   draft-ietf-atompub-protocol-02 - Incorporates Pace409Response,
   PacePostLocationMust, and PaceSimpleResourcePosting.

   draft-ietf-atompub-protocol-01 - Added in sections on Responses for
   the EditURI.  Allow 2xx for response to EditURI PUTs.  Elided all
   mentions of WSSE.  Started adding in some normative references.
   Added the section "Securing the Atom Protocol".  Clarified that it is
   possible that the PostURI and FeedURI could be the same URI.  Cleaned
   up descriptions for Response codes 400 and 500.

   Rev draft-ietf-atompub-protocol-00 - 5Jul2004 - Renamed the file and
   re-titled the document to conform to IETF submission guidelines.
   Changed MIME type to match the one selected for the Atom format.
   Numerous typographical fixes.  We used to have two 'Introduction'
   sections.  One of them was moved into the Abstract the other absorbed
   the Scope section.  IPR and copyright notifications were added.

   Rev 09 - 10Dec2003 - Added the section on SOAP enabled clients and
   servers.

   Rev 08 - 01Dec2003 - Refactored the specification, merging the
   Introspection file into the feed format.  Also dropped the
   distinction between the type of URI used to create new entries and
   the kind used to create comments.  Dropped user preferences.



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   Rev 07 - 06Aug2003 - Removed the use of the RSD file for auto-
   discovery.  Changed copyright until a final standards body is chosen.
   Changed query parameters for the search facet to all begin with atom-
   to avoid name collisions.  Updated all the Entries to follow the 0.2
   version.  Changed the format of the search results and template file
   to a pure element based syntax.

   Rev 06 - 24Jul2003 - Moved to PUT for updating Entries.  Changed all
   the mime-types to application/x.atom+xml.  Added template editing.
   Changed 'edit-entry' to 'create-entry' in the Introspection file to
   more accurately reflect it's purpose.

   Rev 05 - 17Jul2003 - Renamed everything Echo into Atom.  Added
   version numbers in the Revision history.  Changed all the mime-types
   to application/atom+xml.

   Rev 04 - 15Jul2003 - Updated the RSD version used from 0.7 to 1.0.
   Change the method of deleting an Entry from POSTing <delete/> to
   using the HTTP DELETE verb.  Also changed the query interface to GET
   instead of POST.  Moved Introspection Discovery to be up under
   Introspection.  Introduced the term 'facet' for the services listed
   in the Introspection file.

   Rev 03 - 10Jul2003 - Added a link to the Wiki near the front of the
   document.  Added a section on finding an Entry.  Retrieving an Entry
   now broken out into it's own section.  Changed the HTTP status code
   for a successful editing of an Entry to 205.

   Rev 02 - 7Jul2003 - Entries are no longer returned from POSTs,
   instead they are retrieved via GET.  Cleaned up figure titles, as
   they are rendered poorly in HTML.  All content-types have been
   changed to application/atom+xml.

   Rev 01 - 5Jul2003 - Renamed from EchoAPI.html to follow the more
   commonly used format: draft-gregorio-NN.html.  Renamed all references
   to URL to URI.  Broke out introspection into it's own section.  Added
   the Revision History section.  Added more to the warning that the
   example URIs are not normative.













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Internet-Draft        The Atom Publishing Protocol          October 2005


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
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