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rfc:rfc5023

Network Working Group J. Gregorio, Ed. Request for Comments: 5023 Google Category: Standards Track B. de hOra, Ed.

                                                       NewBay Software
                                                          October 2007
                    The Atom Publishing Protocol

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 The Atom Publishing Protocol (AtomPub) is an application-level
 protocol for publishing and editing Web resources.  The protocol is
 based on HTTP transfer of Atom-formatted representations.  The Atom
 format is documented in the Atom Syndication Format.

Gregorio & de hOra Standards Track [Page 1] RFC 5023 The Atom Publishing Protocol October 2007

Table of Contents

 1. Introduction ....................................................4
 2. Notational Conventions ..........................................4
    2.1. XML-Related Conventions ....................................4
         2.1.1. Referring to Information Items ......................4
         2.1.2. RELAX NG Schema .....................................4
         2.1.3. Use of "xml:base" and "xml:lang" ....................5
 3. Terminology .....................................................5
 4. Protocol Model ..................................................6
    4.1. Identity and Naming ........................................6
    4.2. Documents and Resource Classification ......................7
    4.3. Control and Publishing .....................................8
    4.4. Client Implementation Considerations .......................9
 5. Protocol Operations .............................................9
    5.1. Retrieving a Service Document .............................10
    5.2. Listing Collection Members ................................10
    5.3. Creating a Resource .......................................11
    5.4. Editing a Resource ........................................11
         5.4.1. Retrieving a Resource ..............................11
         5.4.2. Editing a Resource .................................12
         5.4.3. Deleting a Resource ................................12
    5.5. Use of HTTP Response Codes ................................12
 6. Protocol Documents .............................................13
    6.1. Document Types ............................................13
    6.2. Document Extensibility ....................................13
 7. Category Documents .............................................14
    7.1. Example ...................................................14
    7.2. Element Definitions .......................................14
         7.2.1. The "app:categories" Element .......................14
 8. Service Documents ..............................................15
    8.1. Workspaces ................................................16
    8.2. Example ...................................................16
    8.3. Element Definitions .......................................17
         8.3.1. The "app:service" Element ..........................17
         8.3.2. The "app:workspace" Element ........................18
         8.3.3. The "app:collection" Element .......................18
         8.3.4. The "app:accept" Element ...........................19
         8.3.5. Usage in Atom Feed Documents .......................19
         8.3.6. The "app:categories" Element .......................20
 9. Creating and Editing Resources .................................20
    9.1. Member URIs ...............................................20
    9.2. Creating Resources with POST ..............................20
         9.2.1. Example ............................................21
    9.3. Editing Resources with PUT ................................22
    9.4. Deleting Resources with DELETE ............................22
    9.5. Caching and Entity Tags ...................................22
         9.5.1. Example ............................................23

Gregorio & de hOra Standards Track [Page 2] RFC 5023 The Atom Publishing Protocol October 2007

    9.6. Media Resources and Media Link Entries ....................25
         9.6.1. Examples ...........................................26
    9.7. The Slug Header ...........................................30
         9.7.1. Slug Header Syntax .................................31
         9.7.2. Example ............................................31
 10. Listing Collections ...........................................32
    10.1. Collection Partial Lists .................................32
    10.2. The "app:edited" Element .................................33
 11. Atom Format Link Relation Extensions ..........................34
    11.1. The "edit" Link Relation .................................34
    11.2. The "edit-media" Link Relation ...........................34
 12. The Atom Format Type Parameter ................................34
    12.1. The "type" parameter .....................................34
         12.1.1. Conformance .......................................35
 13. Atom Publishing Controls ......................................35
    13.1. The "app:control" Element ................................35
         13.1.1. The "app:draft" Element ...........................36
 14. Securing the Atom Publishing Protocol .........................36
 15. Security Considerations .......................................37
    15.1. Denial of Service ........................................37
    15.2. Replay Attacks ...........................................37
    15.3. Spoofing Attacks .........................................37
    15.4. Linked Resources .........................................38
    15.5. Digital Signatures and Encryption ........................38
    15.6. URIs and IRIs ............................................38
    15.7. Code Injection and Cross Site Scripting ..................39
 16. IANA Considerations ...........................................39
    16.1. Content-Type Registration for 'application/atomcat+xml' ..39
    16.2. Content-Type Registration for 'application/atomsvc+xml' ..40
    16.3. Header Field Registration for 'SLUG' .....................42
    16.4. The Link Relation Registration "edit" ....................42
    16.5. The Link Relation Registration "edit-media" ..............42
    16.6. The Atom Format Media Type Parameter .....................43
 17. References ....................................................43
    17.1. Normative References .....................................43
    17.2. Informative References ...................................44
 Appendix A. Contributors ..........................................46
 Appendix B. RELAX NG Compact Schema ...............................46

Gregorio & de hOra Standards Track [Page 3] RFC 5023 The Atom Publishing Protocol October 2007

1. Introduction

 The Atom Publishing Protocol is an application-level protocol for
 publishing and editing Web Resources using HTTP [RFC2616] and XML 1.0
 [REC-xml].  The protocol supports the creation of Web Resources and
 provides facilities for:
 o  Collections: Sets of Resources, which can be retrieved in whole or
    in part.
 o  Services: Discovery and description of Collections.
 o  Editing: Creating, editing, and deleting Resources.
 The Atom Publishing Protocol is different from many contemporary
 protocols in that the server is given wide latitude in processing
 requests from clients.  See Section 4.4 for more details.

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].

2.1. XML-Related Conventions

2.1.1. Referring to Information Items

 Atom Protocol Document formats are specified in terms of the XML
 Information Set [REC-xml-infoset], serialized as XML 1.0 [REC-xml].
 The Infoset terms "Element Information Item" and "Attribute
 Information Item" are shortened to "element" and "attribute"
 respectively.  Therefore, when this specification uses the term
 "element", it is referring to an Element Information Item, and when
 it uses the term "attribute", it is referring to an Attribute
 Information Item.

2.1.2. RELAX NG Schema

 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.  Complete
 schemas appear in Appendix B.

Gregorio & de hOra Standards Track [Page 4] RFC 5023 The Atom Publishing Protocol October 2007

2.1.3. Use of "xml:base" and "xml:lang"

 XML elements defined by this specification MAY have an "xml:base"
 attribute [REC-xmlbase].  When xml:base is used, it serves the
 function described in Section 5.1.1 of URI Generic Syntax [RFC3986],
 by establishing the base URI (or IRI, Internationalized Resource
 Identifier [RFC3987]) for resolving relative references found within
 the 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
 element and its descendants.  Requirements regarding the content and
 interpretation of "xml:lang" are specified in Section 2.12 of XML 1.0
 [REC-xml].

3. Terminology

 For convenience, this protocol can be referred to as the "Atom
 Protocol" or "AtomPub".  The following terminology is used by this
 specification:
 o  URI - A Uniform Resource Identifier as defined in [RFC3986].  In
    this specification, the phrase "the URI of a document" is
    shorthand for "a URI which, when dereferenced, is expected to
    produce that document as a representation".
 o  IRI - An Internationalized Resource Identifier as defined in
    [RFC3987].  Before an IRI found in a document is used by HTTP, the
    IRI is first converted to a URI.  See Section 4.1.
 o  Resource - A network-accessible data object or service identified
    by an IRI, as defined in [RFC2616].  See [REC-webarch] for further
    discussion on Resources.
 o  relation (or "relation of") - Refers to the "rel" attribute value
    of an atom:link element.
 o  Representation - An entity included with a request or response as
    defined in [RFC2616].
 o  Collection - A Resource that contains a set of Member Resources.
    Collections are represented as Atom Feeds.  See Section 9.

Gregorio & de hOra Standards Track [Page 5] RFC 5023 The Atom Publishing Protocol October 2007

 o  Member (or Member Resource) - A Resource whose IRI is listed in a
    Collection by an atom:link element with a relation of "edit" or
    "edit-media".  See Section 9.1.  The protocol defines two kinds of
    Members:
  • Entry Resource - Members of a Collection that are represented

as Atom Entry Documents, as defined in [RFC4287].

  • Media Resource - Members of a Collection that have

representations other than Atom Entry Documents.

 o  Media Link Entry - An Entry Resource that contains metadata about
    a Media Resource.  See Section 9.6.
 o  Workspace - A named group of Collections.  See Section 8.1.
 o  Service Document - A document that describes the location and
    capabilities of one or more Collections, grouped into Workspaces.
    See Section 8.
 o  Category Document - A document that describes the categories
    allowed in a Collection.  See Section 7.

4. Protocol Model

 The Atom Protocol specifies operations for publishing and editing
 Resources using HTTP.  It uses Atom-formatted representations to
 describe the state and metadata of those Resources.  It defines how
 Collections of Resources can be organized, and it specifies formats
 to support their discovery, grouping and categorization.

4.1. Identity and Naming

 Atom Protocol documents allow the use of IRIs [RFC3987] as well as
 URIs [RFC3986] to identify Resources.  Before an IRI in a document is
 used by HTTP, the IRI is first converted to a URI according to the
 procedure defined in Section 3.1 of [RFC3987].  In accordance with
 that specification, the conversion SHOULD be applied as late as
 possible.  Conversion does not imply Resource creation -- the IRI and
 the URI into which it is converted identify the same Resource.
 While the Atom Protocol specifies the formats of the representations
 that are exchanged and the actions that can be performed on the IRIs
 embedded in those representations, it does not constrain the form of
 the URIs that are used.  HTTP [RFC2616] specifies that the URI space
 of each server is controlled by that server, and this protocol
 imposes no further constraints on that control.

Gregorio & de hOra Standards Track [Page 6] RFC 5023 The Atom Publishing Protocol October 2007

4.2. Documents and Resource Classification

 A Resource whose IRI is listed in a Collection is called a Member
 Resource.  The protocol defines two kinds of Member Resources --
 Entry Resources and Media Resources.  Entry Resources are represented
 as Atom Entry Documents [RFC4287].  Media Resources can have
 representations in any media type.  A Media Resource is described
 within a Collection using an Entry called a Media Link Entry.  This
 diagram shows the classification of Resources within the Atom
 Protocol:
              Member Resources
                     |
              -----------------
             |                 |
       Entry Resources     Media Resources
             |
       Media Link Entry
 The Atom Protocol defines Collection Resources for managing and
 organizing both kinds of Member Resource.  A Collection is
 represented by an Atom Feed Document.  A Collection Feed's Entries
 contain the IRIs of, and metadata about, the Collection's Member
 Resources.  A Collection Feed can contain any number of Entries,
 which might represent all the Members of the Collection, or an
 ordered subset of them (see Section 10.1).  In the diagram of a
 Collection below, there are two Entries.  The first contains the IRI
 of an Entry Resource.  The second contains the IRIs of both a Media
 Resource and a Media Link Entry, which contains the metadata for that
 Media Resource:
   Collection
      |
      o- Entry
      |    |
      |    o- Member Entry IRI (Entry Resource)
      |
      o- Entry
           |
           o- Member Entry IRI (Media Link Entry)
           |
           o- Media IRI        (Media Resource)
 The Atom Protocol does not make a distinction between Feeds used for
 Collections and other Atom Feeds.  The only mechanism that this
 specification supplies for indicating that a Feed is a Collection
 Feed is the presence of the Feed's IRI in a Service Document.

Gregorio & de hOra Standards Track [Page 7] RFC 5023 The Atom Publishing Protocol October 2007

 Service Documents represent server-defined groups of Collections, and
 are used to initialize the process of creating and editing Resources.
 These groups of Collections are called Workspaces.  Workspaces have
 names, but no IRIs, and no specified processing model.  The Service
 Document can indicate which media types, and which categories, a
 Collection will accept.  In the diagram below, there are two
 Workspaces each describing the IRIs, acceptable media types, and
 categories for a Collection:
   Service
      o- Workspace
      |    |
      |    o- Collection
      |         |
      |         o- IRI, categories, media types
      |
      o- Workspace
           |
           o- Collection
                |
                o- IRI, categories, media types

4.3. Control and Publishing

 The Atom Publishing Protocol uses HTTP methods to author Member
 Resources as follows:
 o  GET is used to retrieve a representation of a known Resource.
 o  POST is used to create a new, dynamically named, Resource.  When
    the client submits non-Atom-Entry representations to a Collection
    for creation, two Resources are always created -- a Media Entry
    for the requested Resource, and a Media Link Entry for metadata
    about the Resource that will appear in the Collection.
 o  PUT is used to edit a known Resource.  It is not used for Resource
    creation.
 o  DELETE is used to remove a known Resource.
 The Atom Protocol only covers the creating, editing, and deleting of
 Entry and Media Resources.  Other Resources could be created, edited,
 and deleted as the result of manipulating a Collection, but the
 number of those Resources, their media types, and effects of Atom
 Protocol operations on them are outside the scope of this
 specification.

Gregorio & de hOra Standards Track [Page 8] RFC 5023 The Atom Publishing Protocol October 2007

 Since all aspects of client-server interaction are defined in terms
 of HTTP, [RFC2616] should be consulted for any areas not covered in
 this specification.

4.4. Client Implementation Considerations

 The Atom Protocol imposes few restrictions on the actions of servers.
 Unless a constraint is specified here, servers can be expected to
 vary in behavior, in particular around the manipulation of Atom
 Entries sent by clients.  For example, although this specification
 only defines the expected behavior of Collections with respect to GET
 and POST, this does not imply that PUT, DELETE, PROPPATCH, and others
 are forbidden on Collection Resources -- only that this specification
 does not define what the server's response would be to those methods.
 Similarly, while some HTTP status codes are mentioned explicitly,
 clients ought to be prepared to handle any status code from a server.
 Servers can choose to accept, reject, delay, moderate, censor,
 reformat, translate, relocate, or re-categorize the content submitted
 to them.  Only some of these choices are immediately relayed back to
 the client in responses to client requests; other choices may only
 become apparent later, in the feed or published entries.  The same
 series of requests to two different publishing sites can result in a
 different series of HTTP responses, different resulting feeds, or
 different entry contents.
 As a result, client software has to be written flexibly to accept
 what the server decides are the results of its submissions.  Any
 server response or server content modification not explicitly
 forbidden by this specification or HTTP [RFC2616] is therefore
 allowed.

5. Protocol Operations

 While specific HTTP status codes are shown in the interaction
 diagrams below, an AtomPub client should be prepared to handle any
 status code.  For example, a PUT to a Member URI could result in the
 return of a "204 No Content" status code, which still indicates
 success.

Gregorio & de hOra Standards Track [Page 9] RFC 5023 The Atom Publishing Protocol October 2007

5.1. Retrieving a Service Document

 Client                                     Server
   |                                           |
   |  1.) GET to Service Document URI          |
   |------------------------------------------>|
   |                                           |
   |  2.) 200 Ok                               |
   |      Service Document                     |
   |<------------------------------------------|
   |                                           |
 1.  The client sends a GET request to the URI of the Service
     Document.
 2.  The server responds with a Service Document enumerating the IRIs
     of a group of Collections and the capabilities of those
     Collections supported by the server.  The content of this
     document can vary based on aspects of the client request,
     including, but not limited to, authentication credentials.

5.2. Listing Collection Members

 To list the Members of a Collection, the client sends a GET request
 to the URI of a Collection.  An Atom Feed Document is returned whose
 Entries contain the IRIs of Member Resources.  The returned Feed may
 describe all, or only a partial list, of the Members in a Collection
 (see Section 10).
 Client                          Server
   |                                |
   |  1.) GET to Collection URI     |
   |------------------------------->|
   |                                |
   |  2.) 200 Ok                    |
   |      Atom Feed Document        |
   |<-------------------------------|
   |                                |
 1.  The client sends a GET request to the URI of the Collection.
 2.  The server responds with an Atom Feed Document containing the
     IRIs of the Collection Members.

Gregorio & de hOra Standards Track [Page 10] RFC 5023 The Atom Publishing Protocol October 2007

5.3. Creating a Resource

 Client                                     Server
   |                                           |
   |  1.) POST to Collection URI               |
   |      Member Representation                |
   |------------------------------------------>|
   |                                           |
   |  2.) 201 Created                          |
   |      Location: Member Entry URI           |
   |<------------------------------------------|
   |                                           |
 1.  The client POSTs a representation of the Member to the URI of the
     Collection.
 2.  If the Member Resource was created successfully, the server
     responds with a status code of 201 and a Location header that
     contains the IRI of the newly created Entry Resource.  Media
     Resources could have also been created and their IRIs can be
     found through the Entry Resource.  See Section 9.6 for more
     details.

5.4. Editing a Resource

 Once a Resource has been created and its Member URI is known, that
 URI can be used to retrieve, edit, and delete the Resource.  Section
 11 describes extensions to the Atom Syndication Format used in the
 Atom Protocol for editing purposes.

5.4.1. Retrieving a Resource

 Client                                     Server
   |                                           |
   |  1.) GET to Member URI                    |
   |------------------------------------------>|
   |                                           |
   |  2.) 200 Ok                               |
   |      Member Representation                |
   |<------------------------------------------|
   |                                           |
 1.  The client sends a GET request to the URI of a Member Resource to
     retrieve its representation.
 2.  The server responds with the representation of the Member
     Resource.

Gregorio & de hOra Standards Track [Page 11] RFC 5023 The Atom Publishing Protocol October 2007

5.4.2. Editing a Resource

 Client                                     Server
   |                                           |
   |  1.) PUT to Member URI                    |
   |      Member Representation                |
   |------------------------------------------>|
   |                                           |
   |  2.) 200 OK                               |
   |<------------------------------------------|
 1.  The client sends a PUT request to store a representation of a
     Member Resource.
 2.  If the request is successful, the server responds with a status
     code of 200.

5.4.3. Deleting a Resource

 Client                                     Server
   |                                           |
   |  1.) DELETE to Member URI                 |
   |------------------------------------------>|
   |                                           |
   |  2.) 200 OK                               |
   |<------------------------------------------|
   |                                           |
 1.  The client sends a DELETE request to the URI of a Member
     Resource.
 2.  If the deletion is successful, the server responds with a status
     code of 200.
 A different approach is taken for deleting Media Resources; see
 Section 9.4 for details.

5.5. Use of HTTP Response Codes

 The Atom Protocol uses the response status codes defined in HTTP to
 indicate the success or failure of an operation.  Consult the HTTP
 specification [RFC2616] for detailed definitions of each status code.
 Implementers are asked to note that according to the HTTP
 specification, HTTP 4xx and 5xx response entities SHOULD include a
 human-readable explanation of the error.

Gregorio & de hOra Standards Track [Page 12] RFC 5023 The Atom Publishing Protocol October 2007

6. Protocol Documents

6.1. Document Types

 This specification defines two kinds of documents -- Category
 Documents and Service Documents.
 A Category Document (Section 7) contains lists of categories
 specified using the "atom:category" element from the Atom Syndication
 Format (see Section 4.2.2 of [RFC4287]).
 A Service Document (Section 8) groups available Collections into
 Workspaces.
 The namespace name [REC-xml-names] for either kind of document is:
     http://www.w3.org/2007/app
 Atom Publishing Protocol XML Documents MUST be "namespace-well-
 formed" as specified in Section 7 of [REC-xml-names].
 This specification uses the prefix "app:" for the namespace name.
 The prefix "atom:" is used for "http://www.w3.org/2005/Atom", the
 namespace name of the Atom Syndication Format [RFC4287].  These
 namespace prefixes are not semantically significant.
 This specification does not define any DTDs for Atom Protocol
 formats, and hence does not require them to be "valid" in the sense
 used by [REC-xml].

6.2. Document Extensibility

 Unrecognized markup in an Atom Publishing Protocol document is
 considered "foreign markup" as defined in Section 6 of the Atom
 Syndication Format [RFC4287].  Foreign markup can be used anywhere
 within a Category or Service Document unless it is explicitly
 forbidden.  Processors that encounter foreign markup MUST NOT stop
 processing and MUST NOT signal an error.  Clients SHOULD preserve
 foreign markup when transmitting such documents.
 The namespace name "http://www.w3.org/2007/app" is reserved for
 forward-compatible revisions of the Category and Service Document
 types.  This does not exclude the addition of elements and attributes
 that might not be recognized by processors conformant to this
 specification.  Such unrecognized markup from the
 "http://www.w3.org/2007/app" namespace MUST be treated as foreign
 markup.

Gregorio & de hOra Standards Track [Page 13] RFC 5023 The Atom Publishing Protocol October 2007

7. Category Documents

 Category Documents contain lists of categories described using the
 "atom:category" element from the Atom Syndication Format [RFC4287].
 Categories can also appear in Service Documents, where they indicate
 the categories allowed in a Collection (see Section 8.3.6).
 Category Documents are identified with the "application/atomcat+xml"
 media type (see Section 16.1).

7.1. Example

     <?xml version="1.0" ?>
     <app:categories
         xmlns:app="http://www.w3.org/2007/app"
         xmlns:atom="http://www.w3.org/2005/Atom"
         fixed="yes" scheme="http://example.com/cats/big3">
       <atom:category term="animal" />
       <atom:category term="vegetable" />
       <atom:category term="mineral" />
     </app:categories>
 This Category Document contains atom:category elements, with the
 terms 'animal', 'vegetable', and 'mineral'.  None of the categories
 use the "label" attribute defined in [RFC4287].  They all inherit the
 "http://example.com/cats/big3" "scheme" attribute declared on the
 app:categories element.  Therefore if the 'mineral' category were to
 appear in an Atom Entry or Feed Document, it would appear as:
 <atom:category scheme="http://example.com/cats/big3" term="mineral"/>

7.2. Element Definitions

7.2.1. The "app:categories" Element

 The root of a Category Document is the "app:categories" element.  An
 app:categories element can contain zero or more atom:category
 elements from the Atom Syndication Format [RFC4287] namespace
 ("http://www.w3.org/2005/Atom").
 An atom:category child element that has no "scheme" attribute
 inherits the attribute from its app:categories parent.  An atom:
 category child element with an existing "scheme" attribute does not
 inherit the "scheme" value of its app:categories parent element.

Gregorio & de hOra Standards Track [Page 14] RFC 5023 The Atom Publishing Protocol October 2007

 atomCategory =
     element atom:category {
        atomCommonAttributes,
        attribute term { text },
        attribute scheme { atomURI }?,
        attribute label { text }?,
        undefinedContent
     }
 appInlineCategories =
     element app:categories {
         attribute fixed { "yes" | "no" }?,
         attribute scheme { atomURI }?,
         (atomCategory*,
         undefinedContent)
     }
 appOutOfLineCategories =
     element app:categories {
         attribute href { atomURI },
         undefinedContent
     }
 appCategories = appInlineCategories | appOutOfLineCategories

7.2.1.1. Attributes of "app:categories"

 The app:categories element can contain a "fixed" attribute, with a
 value of either "yes" or "no", indicating whether the list of
 categories is a fixed or an open set.  The absence of the "fixed"
 attribute is equivalent to the presence of a "fixed" attribute with a
 value of "no".
 Alternatively, the app:categories element MAY contain an "href"
 attribute, whose value MUST be an IRI reference identifying a
 Category Document.  If the "href" attribute is provided, the app:
 categories element MUST be empty and MUST NOT have the "fixed" or
 "scheme" attributes.

8. Service Documents

 For authoring to commence, a client needs to discover the
 capabilities and locations of the available Collections.  Service
 Documents are designed to support this discovery process.
 How Service Documents are discovered is not defined in this
 specification.

Gregorio & de hOra Standards Track [Page 15] RFC 5023 The Atom Publishing Protocol October 2007

 Service Documents are identified with the "application/atomsvc+xml"
 media type (see Section 16.2).

8.1. Workspaces

 A Service Document groups Collections into Workspaces.  Operations on
 Workspaces, such as creation or deletion, are not defined by this
 specification.  This specification assigns no meaning to Workspaces;
 that is, a Workspace does not imply any specific processing
 assumptions.
 There is no requirement that a server support multiple Workspaces.
 In addition, a Collection MAY appear in more than one Workspace.

8.2. Example

 <?xml version="1.0" encoding='utf-8'?>
 <service xmlns="http://www.w3.org/2007/app"
          xmlns:atom="http://www.w3.org/2005/Atom">
   <workspace>
     <atom:title>Main Site</atom:title>
     <collection
         href="http://example.org/blog/main" >
       <atom:title>My Blog Entries</atom:title>
       <categories
          href="http://example.com/cats/forMain.cats" />
     </collection>
     <collection
         href="http://example.org/blog/pic" >
       <atom:title>Pictures</atom:title>
       <accept>image/png</accept>
       <accept>image/jpeg</accept>
       <accept>image/gif</accept>
     </collection>
   </workspace>
   <workspace>
     <atom:title>Sidebar Blog</atom:title>
     <collection
         href="http://example.org/sidebar/list" >
       <atom:title>Remaindered Links</atom:title>
       <accept>application/atom+xml;type=entry</accept>
       <categories fixed="yes">
         <atom:category
           scheme="http://example.org/extra-cats/"
           term="joke" />
         <atom:category
           scheme="http://example.org/extra-cats/"
           term="serious" />

Gregorio & de hOra Standards Track [Page 16] RFC 5023 The Atom Publishing Protocol October 2007

       </categories>
     </collection>
   </workspace>
 </service>
 The Service Document above describes two Workspaces.  The first
 Workspace is called "Main Site", and has two Collections called "My
 Blog Entries" and "Pictures", whose IRIs are
 "http://example.org/blog/main" and "http://example.org/blog/pic"
 respectively.  The "Pictures" Collection includes three "accept"
 elements indicating the types of image files the client can send to
 the Collection to create new Media Resources (entries associated with
 Media Resources are discussed in Section 9.6).
 The second Workspace is called "Sidebar Blog" and has a single
 Collection called "Remaindered Links" whose IRI is
 "http://example.org/sidebar/list".  The Collection has an "accept"
 element whose content is "application/atom+xml;type=entry",
 indicating it will accept Atom Entries from a client.
 Within each of the two Entry Collections, the "categories" element
 provides a list of available categories for Member Entries.  In the
 "My Blog Entries" Collection, the list of available categories is
 available through the "href" attribute.  The "Sidebar Blog"
 Collection provides a category list within the Service Document, but
 states the list is fixed, signaling a request from the server that
 Entries be POSTed using only those two categories.

8.3. Element Definitions

8.3.1. The "app:service" Element

 The root of a Service Document is the "app:service" element.
 The app:service element is the container for service information
 associated with one or more Workspaces.  An app:service element MUST
 contain one or more app:workspace elements.
 namespace app = "http://www.w3.org/2007/app"
 start = appService
 appService =
    element app:service {
       appCommonAttributes,
       ( appWorkspace+
         & extensionElement* )
    }

Gregorio & de hOra Standards Track [Page 17] RFC 5023 The Atom Publishing Protocol October 2007

8.3.2. The "app:workspace" Element

 Workspaces are server-defined groups of Collections.  The "app:
 workspace" element contains zero or more app:collection elements
 describing the Collections of Resources available for editing.
 appWorkspace =
    element app:workspace {
       appCommonAttributes,
       ( atomTitle
         & appCollection*
         & extensionSansTitleElement* )
    }
 atomTitle = element atom:title { atomTextConstruct }

8.3.2.1. The "atom:title" Element

 The app:workspace element MUST contain one "atom:title" element (as
 defined in [RFC4287]), giving a human-readable title for the
 Workspace.

8.3.3. The "app:collection" Element

 The "app:collection" element describes a Collection.  The app:
 collection element MUST contain one atom:title element.
 The app:collection element MAY contain any number of app:accept
 elements, indicating the types of representations accepted by the
 Collection.  The order of such elements is not significant.
 The app:collection element MAY contain any number of app:categories
 elements.
 appCollection =
    element app:collection {
       appCommonAttributes,
       attribute href { atomURI  },
       ( atomTitle
         & appAccept*
         & appCategories*
         & extensionSansTitleElement* )
    }

8.3.3.1. The "href" Attribute

 The app:collection element MUST contain an "href" attribute, whose
 value gives the IRI of the Collection.

Gregorio & de hOra Standards Track [Page 18] RFC 5023 The Atom Publishing Protocol October 2007

8.3.3.2. The "atom:title" Element

 The "atom:title" element is defined in [RFC4287] and gives a human-
 readable title for the Collection.

8.3.4. The "app:accept" Element

 The content of an "app:accept" element value is a media range as
 defined in [RFC2616].  The media range specifies a type of
 representation that can be POSTed to a Collection.
 The app:accept element is similar to the HTTP Accept request-header
 [RFC2616].  Media type parameters are allowed within app:accept, but
 app:accept has no notion of preference -- "accept-params" or "q"
 arguments, as specified in Section 14.1 of [RFC2616] are not
 significant.
 White space (as defined in [REC-xml]) around the app:accept element's
 media range is insignificant and MUST be ignored.
 A value of "application/atom+xml;type=entry" MAY appear in any app:
 accept list of media ranges and indicates that Atom Entry Documents
 can be POSTed to the Collection.  If no app:accept element is
 present, clients SHOULD treat this as equivalent to an app:accept
 element with the content "application/atom+xml;type=entry".
 If one app:accept element exists and is empty, clients SHOULD assume
 that the Collection does not support the creation of new Entries.
 appAccept =
    element app:accept {
          appCommonAttributes,
          ( text? )
    }

8.3.5. Usage in Atom Feed Documents

 The app:collection element MAY appear as a child of an atom:feed or
 atom:source element in an Atom Feed Document.  Its content identifies
 a Collection by which new Entries can be added to appear in the feed.
 When it appears in an atom:feed or atom:source element, the app:
 collection element is considered foreign markup as defined in Section
 6 of [RFC4287].

Gregorio & de hOra Standards Track [Page 19] RFC 5023 The Atom Publishing Protocol October 2007

8.3.6. The "app:categories" Element

 The "app:categories" element provides a list of the categories that
 can be applied to the members of a Collection.  See Section 7.2.1 for
 the detailed definition of app:categories.
 The server MAY reject attempts to create or store members whose
 categories are not present in its categories list.  A Collection that
 indicates the category set is open SHOULD NOT reject otherwise
 acceptable members whose categories are not in its categories list.
 The absence of an app:categories element means that the category
 handling of the Collection is unspecified.  A "fixed" category list
 that contains zero categories indicates the Collection does not
 accept category data.

9. Creating and Editing Resources

9.1. Member URIs

 The Member URI allows clients to retrieve, edit, and delete a Member
 Resource using HTTP's GET, PUT, and DELETE methods.  Entry Resources
 are represented as Atom Entry documents.
 Member URIs appear in two places.  They are returned in a Location
 header after successful Resource creation using POST, as described in
 Section 9.2 below.  They can also appear in a Collection Feed's
 Entries, as atom:link elements with a link relation of "edit".
 A Member Entry SHOULD contain such an atom:link element with a link
 relation of "edit", which indicates the Member URI.

9.2. Creating Resources with POST

 To add members to a Collection, clients send POST requests to the URI
 of the Collection.
 Successful member creation is indicated with a 201 ("Created")
 response code.  When the Collection responds with a status code of
 201, it SHOULD also return a response body, which MUST be an Atom
 Entry Document representing the newly created Resource.  Since the
 server is free to alter the POSTed Entry, for example, by changing
 the content of the atom:id element, returning the Entry can be useful
 to the client, enabling it to correlate the client and server views
 of the new Entry.
 When a Member Resource is created, its Member Entry URI MUST be
 returned in a Location header in the Collection's response.

Gregorio & de hOra Standards Track [Page 20] RFC 5023 The Atom Publishing Protocol October 2007

 If the creation request contained an Atom Entry Document, and the
 subsequent response from the server contains a Content-Location
 header that matches the Location header character-for-character, then
 the client is authorized to interpret the response entity as being a
 complete representation of the newly created Entry.  Without a
 matching Content-Location header, the client MUST NOT assume the
 returned entity is a complete representation of the created Resource.
 The request body sent with the POST need not be an Atom Entry.  For
 example, it might be a picture or a movie.  Collections MAY return a
 response with a status code of 415 ("Unsupported Media Type") to
 indicate that the media type of the POSTed entity is not allowed or
 supported by the Collection.  For a discussion of the issues in
 creating such content, see Section 9.6.

9.2.1. Example

 Below, the client sends a POST request containing an Atom Entry
 representation using the URI of the Collection:
     POST /edit/ HTTP/1.1
     Host: example.org
     User-Agent: Thingio/1.0
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
     Content-Type: application/atom+xml;type=entry
     Content-Length: nnn
     Slug: First Post
     <?xml version="1.0"?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>Atom-Powered Robots Run Amok</title>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
       <updated>2003-12-13T18:30:02Z</updated>
       <author><name>John Doe</name></author>
       <content>Some text.</content>
     </entry>
 The server signals a successful creation with a status code of 201.
 The response includes a Location header indicating the Member Entry
 URI of the Atom Entry, and a representation of that Entry in the body
 of the response.
     HTTP/1.1 201 Created
     Date: Fri, 7 Oct 2005 17:17:11 GMT
     Content-Length: nnn
     Content-Type: application/atom+xml;type=entry;charset="utf-8"
     Location: http://example.org/edit/first-post.atom
     ETag: "c180de84f991g8"

Gregorio & de hOra Standards Track [Page 21] RFC 5023 The Atom Publishing Protocol October 2007

     <?xml version="1.0"?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>Atom-Powered Robots Run Amok</title>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
       <updated>2003-12-13T18:30:02Z</updated>
       <author><name>John Doe</name></author>
       <content>Some text.</content>
       <link rel="edit"
           href="http://example.org/edit/first-post.atom"/>
     </entry>
 The Entry created and returned by the Collection might not match the
 Entry POSTed by the client.  A server MAY change the values of
 various elements in the Entry, such as the atom:id, atom:updated, and
 atom:author values, and MAY choose to remove or add other elements
 and attributes, or change element content and attribute values.

9.3. Editing Resources with PUT

 To edit a Member Resource, a client sends a PUT request to its Member
 URI, as specified in [RFC2616].
 To avoid unintentional loss of data when editing Member Entries or
 Media Link Entries, an Atom Protocol client SHOULD preserve all
 metadata that has not been intentionally modified, including unknown
 foreign markup as defined in Section 6 of [RFC4287].

9.4. Deleting Resources with DELETE

 To delete a Member Resource, a client sends a DELETE request to its
 Member URI, as specified in [RFC2616].  The deletion of a Media Link
 Entry SHOULD result in the deletion of the corresponding Media
 Resource.

9.5. Caching and Entity Tags

 Implementers are advised to pay attention to cache controls and to
 make use of the mechanisms available in HTTP when editing Resources,
 in particular, entity-tags as outlined in [NOTE-detect-lost-update].
 Clients are not assured to receive the most recent representations of
 Collection Members using GET if the server is authorizing
 intermediaries to cache them.

Gregorio & de hOra Standards Track [Page 22] RFC 5023 The Atom Publishing Protocol October 2007

9.5.1. Example

 Below, the client creates a Member Entry using POST:
     POST /myblog/entries HTTP/1.1
     Host: example.org
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
     Content-Type: application/atom+xml;type=entry
     Content-Length: nnn
     Slug: First Post
     <?xml version="1.0" ?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>Atom-Powered Robots Run Amok</title>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
       <updated>2007-02-123T17:09:02Z</updated>
       <author><name>Captain Lansing</name></author>
       <content>It's something moving... solid metal</content>
     </entry>
 The server signals a successful creation with a status code of 201,
 and returns an ETag header in the response.  Because, in this case,
 the server returned a Content-Location header and Location header
 with the same value, the returned Entry representation can be
 understood to be a complete representation of the newly created Entry
 (see Section 9.2).
     HTTP/1.1 201 Created
     Date: Fri, 23 Feb 2007 21:17:11 GMT
     Content-Length: nnn
     Content-Type: application/atom+xml;type=entry
     Location: http://example.org/edit/first-post.atom
     Content-Location: http://example.org/edit/first-post.atom
     ETag: "e180ee84f0671b1"
     <?xml version="1.0" ?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>Atom-Powered Robots Run Amok</title>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
       <updated>2007-02-123T17:09:02Z</updated>
       <author><name>Captain Lansing</name></author>
       <content>It's something moving... solid metal</content>
     </entry>
 The client can, if it wishes, use the returned ETag value to later
 construct a "Conditional GET" as defined in [RFC2616].  In this case,
 prior to editing, the client sends the ETag value for the Member
 using the If-None-Match header.

Gregorio & de hOra Standards Track [Page 23] RFC 5023 The Atom Publishing Protocol October 2007

     GET /edit/first-post.atom HTTP/1.1
     Host: example.org
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
     If-None-Match: "e180ee84f0671b1"
 If the Entry has not been modified, the response will be a status
 code of 304 ("Not Modified").  This allows the client to determine
 whether it still has the most recent representation of the Entry at
 the time of editing.
     HTTP/1.1 304 Not Modified
     Date: Sat, 24 Feb 2007 13:17:11 GMT
 After editing, the client can PUT the Entry and send the ETag entity
 value in an If-Match header, informing the server to accept the entry
 on the condition that the entity value sent still matches the
 server's.
     PUT /edit/first-post.atom HTTP/1.1
     Host: example.org
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
     Content-Type: application/atom+xml;type=entry
     Content-Length: nnn
     If-Match: "e180ee84f0671b1"
     <?xml version="1.0" ?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>Atom-Powered Robots Run Amok</title>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
       <updated>2007-02-24T16:34:06Z</updated>
       <author><name>Captain Lansing</name></author>
       <content>Update: it's a hoax!</content>
     </entry>
 The server however has since received a more recent copy than the
 client's, and it responds with a status code of 412 ("Precondition
 Failed").
     HTTP/1.1 412 Precondition Failed
     Date: Sat, 24 Feb 2007 16:34:11 GMT
 This informs the client that the server has a more recent version of
 the Entry and will not allow the sent entity to be stored.

Gregorio & de hOra Standards Track [Page 24] RFC 5023 The Atom Publishing Protocol October 2007

9.6. Media Resources and Media Link Entries

 A client can POST Media Resources as well as Entry Resources to a
 Collection.  If a server accepts such a request, then it MUST create
 two new Resources -- one that corresponds to the entity sent in the
 request, called the Media Resource, and an associated Member Entry,
 called the Media Link Entry.  Media Link Entries are represented as
 Atom Entries, and appear in the Collection.
 The Media Link Entry contains the metadata and IRI of the (perhaps
 non-textual) Media Resource.  The Media Link Entry thus makes the
 metadata about the Media Resource separately available for retrieval
 and alteration.
 The server can signal the media types it will accept using the app:
 accept element in the Service Document, as specified in Section
 8.3.4.
 Successful responses to creation requests MUST include the URI of the
 Media Link Entry in the Location header.  The Media Link Entry SHOULD
 contain an atom:link element with a link relation of "edit-media"
 that contains the Media Resource IRI.  The Media Link Entry MUST have
 an atom:content element with a "src" attribute.  The value of the
 "src" attribute is an IRI for the newly created Media Resource.  It
 is OPTIONAL that the IRI of the "src" attribute on the atom:content
 element be the same as the Media Resource IRI.  For example, the
 "src" attribute value might instead be a link into a static cache or
 content distribution network and not the Media Resource IRI.
 Implementers are asked to note that [RFC4287] specifies that Atom
 Entries MUST contain an atom:summary element.  Thus, upon successful
 creation of a Media Link Entry, a server MAY choose to populate the
 atom:summary element (as well as any other mandatory elements such as
 atom:id, atom:author, and atom:title) with content derived from the
 POSTed entity or from any other source.  A server might not allow a
 client to modify the server-selected values for these elements.
 For Resource creation, this specification only defines cases where
 the POST body has an Atom Entry entity declared as an Atom media type
 ("application/atom+xml"), or a non-Atom entity declared as a non-Atom
 media type.  When a client is POSTing an Atom Entry to a Collection,
 it may use a media type of either "application/atom+xml" or
 "application/atom +xml;type=entry".  This specification does not
 specify any request semantics or server behavior in the case where
 the POSTed media type is "application/atom+xml" but the body is
 something other than an Atom Entry.  In particular, what happens on
 POSTing an Atom Feed Document to a Collection using the "application/
 atom+xml" media type is undefined.

Gregorio & de hOra Standards Track [Page 25] RFC 5023 The Atom Publishing Protocol October 2007

 The Atom Protocol does not specify a means to create multiple
 representations of the same Resource (for example, a PNG and a JPG of
 the same image) either on creation or editing.

9.6.1. Examples

 Below, the client sends a POST request containing a PNG image to the
 URI of a Collection that accepts PNG images:
     POST /edit/ HTTP/1.1
     Host: media.example.org
     Content-Type: image/png
     Slug: The Beach
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
     Content-Length: nnn
     ...binary data...
 The server signals a successful creation with a status code of 201.
 The response includes a Location header indicating the Member URI of
 the Media Link Entry and a representation of that entry in the body
 of the response.  The Media Link Entry includes a content element
 with a "src" attribute.  It also contains a link with a link relation
 of "edit-media", specifying the IRI to be used for modifying the
 Media Resource.
     HTTP/1.1 201 Created
     Date: Fri, 7 Oct 2005 17:17:11 GMT
     Content-Length: nnn
     Content-Type: application/atom+xml;type=entry;charset="utf-8"
     Location: http://example.org/media/edit/the_beach.atom
     <?xml version="1.0"?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>The Beach</title>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
       <updated>2005-10-07T17:17:08Z</updated>
       <author><name>Daffy</name></author>
       <summary type="text" />
       <content type="image/png"
          src="http://media.example.org/the_beach.png"/>
       <link rel="edit-media"
          href="http://media.example.org/edit/the_beach.png" />
       <link rel="edit"
          href="http://example.org/media/edit/the_beach.atom" />
     </entry>

Gregorio & de hOra Standards Track [Page 26] RFC 5023 The Atom Publishing Protocol October 2007

 Later, the client sends a PUT request containing the new PNG using
 the URI indicated in the Media Link Entry's "edit-media" link:
     PUT /edit/the_beach.png HTTP/1.1
     Host: media.example.org
     Content-Type: image/png
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
     Content-Length: nnn
     ...binary data...
 The server signals a successful edit with a status code of 200.
     HTTP/1.1 200 Ok
     Date: Fri, 8 Oct 2006 17:17:11 GMT
 The client can edit the metadata for the picture.  First GET the
 Media Link Entry:
     GET /media/edit/the_beach.atom HTTP/1.1
     Host: example.org
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
 The Media Link Entry is returned.
     HTTP/1.1 200 Ok
     Date: Fri, 7 Oct 2005 17:18:11 GMT
     Content-Length: nnn
     Content-Type: application/atom+xml;type=entry;charset="utf-8"
     ETag: "c181bb840673b5"
     <?xml version="1.0"?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>The Beach</title>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
       <updated>2005-10-07T17:17:08Z</updated>
       <author><name>Daffy</name></author>
       <summary type="text" />
       <content type="image/png"
          src="http://media.example.org/the_beach.png"/>
       <link rel="edit-media"
          href="http://media.example.org/edit/the_beach.png" />
       <link rel="edit"
          href="http://example.org/media/edit/the_beach.atom" />
     </entry>
 The metadata can be updated, in this case to add a summary, and then
 PUT back to the server.

Gregorio & de hOra Standards Track [Page 27] RFC 5023 The Atom Publishing Protocol October 2007

     PUT /media/edit/the_beach.atom HTTP/1.1
     Host: example.org
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
     Content-Type: application/atom+xml;type=entry
     Content-Length: nnn
     If-Match: "c181bb840673b5"
     <?xml version="1.0"?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>The Beach</title>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
       <updated>2005-10-07T17:17:08Z</updated>
       <author><name>Daffy</name></author>
       <summary type="text">
           A nice sunset picture over the water.
       </summary>
       <content type="image/png"
          src="http://media.example.org/the_beach.png"/>
       <link rel="edit-media"
          href="http://media.example.org/edit/the_beach.png" />
       <link rel="edit"
          href="http://example.org/media/edit/the_beach.atom" />
     </entry>
 The update was successful.
     HTTP/1.1 200 Ok
     Date: Fri, 7 Oct 2005 17:19:11 GMT
     Content-Length: 0
 Multiple Media Resources can be added to the Collection.
     POST /edit/ HTTP/1.1
     Host: media.example.org
     Content-Type: image/png
     Slug: The Pier
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
     Content-Length: nnn
     ...binary data...
 The Resource is created successfully.
     HTTP/1.1 201 Created
     Date: Fri, 7 Oct 2005 17:17:11 GMT
     Content-Length: nnn
     Content-Type: application/atom+xml;type=entry;charset="utf-8"
     Location: http://example.org/media/edit/the_pier.atom

Gregorio & de hOra Standards Track [Page 28] RFC 5023 The Atom Publishing Protocol October 2007

     <?xml version="1.0"?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>The Pier</title>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efe6b</id>
       <updated>2005-10-07T17:26:43Z</updated>
       <author><name>Daffy</name></author>
       <summary type="text" />
       <content type="image/png"
          src="http://media.example.org/the_pier.png"/>
       <link rel="edit-media"
          href="http://media.example.org/edit/the_pier.png" />
       <link rel="edit"
          href="http://example.org/media/edit/the_pier.atom" />
     </entry>
 The client can now create a new Atom Entry in the blog Entry
 Collection that references the two newly created Media Resources.
     POST /blog/ HTTP/1.1
     Host: example.org
     Content-Type: application/atom+xml;type=entry
     Slug: A day at the beach
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
     Content-Length: nnn
     <?xml version="1.0"?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>A fun day at the beach</title>
       <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6b</id>
       <updated>2005-10-07T17:40:02Z</updated>
       <author><name>Daffy</name></author>
       <content type="xhtml">
           <xhtml:div xmlns:xhtml="http://www.w3.org/1999/xhtml">
               <xhtml:p>We had a good day at the beach.
                   <xhtml:img alt="the beach"
                       src="http://media.example.org/the_beach.png"/>
               </xhtml:p>
               <xhtml:p>Later we walked down to the pier.
                   <xhtml:img  alt="the pier"
                       src="http://media.example.org/the_pier.png"/>
               </xhtml:p>
           </xhtml:div>
       </content>
     </entry>
 The Resource is created successfully.

Gregorio & de hOra Standards Track [Page 29] RFC 5023 The Atom Publishing Protocol October 2007

     HTTP/1.1 200 Ok
     Date: Fri, 7 Oct 2005 17:20:11 GMT
     Content-Length: nnn
     Content-Type: application/atom+xml;type=entry;charset="utf-8"
     Location: http://example.org/blog/atom/a-day-at-the-beach.atom
     <?xml version="1.0"?>
     <entry xmlns="http://www.w3.org/2005/Atom">
       <title>A fun day at the beach</title>
       <id>http://example.org/blog/a-day-at-the-beach.xhtml</id>
       <updated>2005-10-07T17:43:07Z</updated>
       <author><name>Daffy</name></author>
       <content type="xhtml">
           <xhtml:div xmlns:xhtml="http://www.w3.org/1999/xhtml">
               <xhtml:p>We had a good day at the beach.
                   <xhtml:img alt="the beach"
                      src="http://media.example.org/the_beach.png"/>
               </xhtml:p>
               <xhtml:p>Later we walked down to the pier.
                   <xhtml:img alt="the pier"
                      src="http://media.example.org/the_pier.png"/>
               </xhtml:p>
           </xhtml:div>
       </content>
       <link rel="edit"
         href="http://example.org/blog/edit/a-day-at-the-beach.atom"/>
       <link rel="alternate" type="text/html"
         href="http://example.org/blog/a-day-at-the-beach.html"/>
     </entry>
 Note that the returned Entry contains a link with a relation of
 "alternate" that points to the associated HTML page that was created
 -- this is not required by this specification, but is included to
 show the kinds of changes a server can make to an Entry.

9.7. The Slug Header

 Slug is an HTTP entity-header whose presence in a POST to a
 Collection constitutes a request by the client to use the header's
 value as part of any URIs that would normally be used to retrieve the
 to-be-created Entry or Media Resources.
 Servers MAY use the value of the Slug header when creating the Member
 URI of the newly created Resource, for instance, by using some or all
 of the words in the value for the last URI segment.  Servers MAY also
 use the value when creating the atom:id, or as the title of a Media
 Link Entry (see Section 9.6).

Gregorio & de hOra Standards Track [Page 30] RFC 5023 The Atom Publishing Protocol October 2007

 Servers MAY choose to ignore the Slug entity-header.  Servers MAY
 alter the header value before using it.  For instance, a server might
 filter out some characters or replace accented letters with non-
 accented ones, replace spaces with underscores, change case, and so
 on.

9.7.1. Slug Header Syntax

 The syntax of the Slug header is defined using the augmented BNF
 syntax defined in Section 2.1 of [RFC2616]:
     LWS      = <defined in Section 2.2 of [RFC2616]>
     slugtext = %x20-7E | LWS
     Slug     = "Slug" ":" *slugtext
 The field value is the percent-encoded value of the UTF-8 encoding of
 the character sequence to be included (see Section 2.1 of [RFC3986]
 for the definition of percent encoding, and [RFC3629] for the
 definition of the UTF-8 encoding).
 Implementation note: to produce the field value from a character
 sequence, first encode it using the UTF-8 encoding, then encode all
 octets outside the ranges %20-24 and %26-7E using percent encoding
 (%25 is the ASCII encoding of "%", thus it needs to be escaped).  To
 consume the field value, first reverse the percent encoding, then run
 the resulting octet sequence through a UTF-8 decoding process.

9.7.2. Example

 Here is an example of the Slug header that uses percent-encoding to
 represent the Unicode character U+00E8 (LATIN SMALL LETTER E WITH
 GRAVE):
     POST /myblog/entries HTTP/1.1
     Host: example.org
     Content-Type: image/png
     Slug: The Beach at S%C3%A8te
     Authorization: Basic ZGFmZnk6c2VjZXJldA==
     Content-Length: nnn
     ...binary data...
 See Section 9.2.1 for an example of the Slug header applied to the
 creation of an Entry Resource.

Gregorio & de hOra Standards Track [Page 31] RFC 5023 The Atom Publishing Protocol October 2007

10. Listing Collections

 Collection Resources MUST provide representations in the form of Atom
 Feed Documents whose Entries contain the IRIs of the Members in the
 Collection.  No distinction is made between Collection Feeds and
 other kinds of Feeds -- a Feed might act both as a 'public' feed for
 subscription purposes and as a Collection Feed.
 Each Entry in the Feed Document SHOULD have an atom:link element with
 a relation of "edit" (see Section 11.1).
 The Entries in the returned Atom Feed SHOULD be ordered by their
 "app:edited" property, with the most recently edited Entries coming
 first in the document order.  The app:edited value is not equivalent
 to the HTTP Last-Modified header and cannot be used to determine the
 freshness of cached responses.
 Clients MUST NOT assume that an Atom Entry returned in the Feed is a
 full representation of an Entry Resource and SHOULD perform a GET on
 the URI of the Member Entry before editing it.  See Section 9.5 for a
 discussion on the implications of cache control directives when
 obtaining entries.

10.1. Collection Partial Lists

 Collections can contain large numbers of Resources.  A client such as
 a web spider or web browser might be overwhelmed if the response to a
 GET contained every Entry in a Collection -- in turn the server might
 also waste bandwidth and processing time on generating a response
 that cannot be handled.  For this reason, servers MAY respond to
 Collection GET requests with a Feed Document containing a partial
 list of the Collection's members, and a link to the next partial list
 feed, if it exists.  The first such partial list returned MUST
 contain the most recently edited member Resources and MUST have an
 atom:link with a "next" relation whose "href" value is the URI of the
 next partial list of the Collection.  This next partial list will
 contain the next most recently edited set of Member Resources (and an
 atom:link to the following partial list if it exists).
 In addition to the "next" relation, partial list feeds MAY contain
 link elements with "rel" attribute values of "previous", "first", and
 "last", that can be used to navigate through the complete set of
 entries in the Collection.
 For instance, suppose a client is supplied the URI
 "http://example.org/entries/go" of a Collection of Member Entries,
 where the server as a matter of policy avoids generating Feed
 Documents containing more than 10 Entries.  The Atom Feed Document

Gregorio & de hOra Standards Track [Page 32] RFC 5023 The Atom Publishing Protocol October 2007

 for the Collection will then represent the first partial list of a
 set of 10 linked Feed Documents.  The "first" relation references the
 initial Feed Document in the set and the "last" relation references
 the final Feed Document in the set.  Within each document, the
 "previous" and "next" link relations reference the preceding and
 subsequent documents.
   <feed xmlns="http://www.w3.org/2005/Atom">
     <link rel="first"
           href="http://example.org/entries/go" />
     <link rel="next"
           href="http://example.org/entries/2" />
     <link rel="last"
           href="http://example.org/entries/10" />
     ...
   </feed>
 The "previous" and "next" link elements for the partial list feed
 located at "http://example.org/entries/2" would look like this:
   <feed xmlns="http://www.w3.org/2005/Atom">
     <link rel="first"
           href="http://example.org/entries/go" />
     <link rel="previous"
           href="http://example.org/entries/go" />
     <link rel="next"
           href="http://example.org/entries/3" />
     <link rel="last"
           href="http://example.org/entries/10" />
     ...
   </feed>

10.2. The "app:edited" Element

 The "app:edited" element is a Date construct (as defined by
 [RFC4287]), whose content indicates the last time an Entry was
 edited.  If the entry has not been edited yet, the content indicates
 the time it was created.  Atom Entry elements in Collection Documents
 SHOULD contain one app:edited element, and MUST NOT contain more than
 one.
 appEdited = element app:edited ( atomDateConstruct )
 The server SHOULD change the value of this element every time an
 Entry Resource or an associated Media Resource has been edited.

Gregorio & de hOra Standards Track [Page 33] RFC 5023 The Atom Publishing Protocol October 2007

11. Atom Format Link Relation Extensions

11.1. The "edit" Link Relation

 This specification adds the value "edit" to the Atom Registry of Link
 Relations (see Section 7.1 of [RFC4287]).  The value of "edit"
 specifies that the value of the href attribute is the IRI of an
 editable Member Entry.  When appearing within an atom:entry, the href
 IRI can be used to retrieve, update, and delete the Resource
 represented by that Entry.  An atom:entry MUST NOT contain more than
 one "edit" link relation.

11.2. The "edit-media" Link Relation

 This specification adds the value "edit-media" to the Atom Registry
 of Link Relations (see Section 7.1 of [RFC4287]).  When appearing
 within an atom:entry, the value of the href attribute is an IRI that
 can be used to modify a Media Resource associated with that Entry.
 An atom:entry element MAY contain zero or more "edit-media" link
 relations.  An atom:entry MUST NOT contain more than one atom:link
 element with a "rel" attribute value of "edit-media" that has the
 same "type" and "hreflang" attribute values.  All "edit-media" link
 relations in the same Entry reference the same Resource.  If a client
 encounters multiple "edit-media" link relations in an Entry then it
 SHOULD choose a link based on the client preferences for "type" and
 "hreflang".  If a client encounters multiple "edit-media" link
 relations in an Entry and has no preference based on the "type" and
 "hreflang" attributes then the client SHOULD pick the first "edit-
 media" link relation in document order.

12. The Atom Format Type Parameter

 The Atom Syndication Format [RFC4287] defines the "application/
 atom+xml" media type to identify both Atom Feed and Atom Entry
 Documents.  Implementation experience has demonstrated that Atom Feed
 and Entry Documents can have different processing models and that
 there are situations where they need to be differentiated.  This
 specification defines a "type" parameter used to differentiate the
 two types of Atom documents.

12.1. The "type" parameter

 This specification defines a new "type" parameter for use with the
 "application/atom+xml" media type.  The "type" parameter has a value
 of "entry" or "feed".
 Neither the parameter name nor its value are case sensitive.

Gregorio & de hOra Standards Track [Page 34] RFC 5023 The Atom Publishing Protocol October 2007

 The value "entry" indicates that the media type identifies an Atom
 Entry Document.  The root element of the document MUST be atom:entry.
 The value "feed" indicates that the media type identifies an Atom
 Feed Document.  The root element of the document MUST be atom:feed.
 If not specified, the type is assumed to be unspecified, requiring
 Atom processors to examine the root element to determine the type of
 Atom document.

12.1.1. Conformance

 New specifications MAY require that the "type" parameter be used to
 identify the Atom Document type.  Producers of Atom Entry Documents
 SHOULD use the "type" parameter regardless of whether or not it is
 mandatory.  Producers of Atom Feed Documents MAY use the parameter.
 Atom processors that do not recognize the "type" parameter MUST
 ignore its value and examine the root element to determine the
 document type.
 Atom processors that do recognize the "type" parameter SHOULD detect
 and report inconsistencies between the parameter's value and the
 actual type of the document's root element.

13. Atom Publishing Controls

 This specification defines an Atom Format Structured Extension, as
 defined in Section 6 of [RFC4287], for publishing control within the
 "http://www.w3.org/2007/app" namespace.

13.1. The "app:control" Element

 namespace app = "http://www.w3.org/2007/app"
  pubControl =
     element app:control {
     atomCommonAttributes,
     pubDraft?
     & extensionElement
  }
  pubDraft =
    element app:draft { "yes" | "no" }

Gregorio & de hOra Standards Track [Page 35] RFC 5023 The Atom Publishing Protocol October 2007

 The "app:control" element MAY appear as a child of an atom:entry that
 is being created or updated via the Atom Publishing Protocol.  The
 app:control element MUST appear only once in an Entry.  The app:
 control element is considered foreign markup as defined in Section 6
 of [RFC4287].
 The app:control element and its child elements MAY be included in
 Atom Feed or Entry Documents.
 The app:control element can contain an "app:draft" element as defined
 below, and it can contain extension elements as defined in Section 6
 of [RFC4287].

13.1.1. The "app:draft" Element

 The inclusion of the "app:draft" element represents a request by the
 client to control the visibility of a Member Resource.  The app:draft
 element MAY be ignored by the server.
 The number of app:draft elements in app:control MUST be zero or one.
 The content of an app:draft element MUST be one of "yes" or "no".  If
 the element contains "no", this indicates a client request that the
 Member Resource be made publicly visible.  If the app:draft element
 is not present, then servers that support the extension MUST behave
 as though an app:draft element containing "no" was sent.

14. Securing the Atom Publishing Protocol

 The Atom Publishing Protocol is based on HTTP.  Authentication
 requirements for HTTP are covered in Section 11 of [RFC2616].
 The use of authentication mechanisms to prevent POSTing or editing by
 unknown or unauthorized clients is RECOMMENDED but not required.
 When authentication is not used, clients and servers are vulnerable
 to trivial spoofing, denial-of-service, and defacement attacks.
 However, in some contexts, this is an acceptable risk.
 The type of authentication deployed is a local decision made by the
 server operator.  Clients are likely to face authentication schemes
 that vary across server deployments.  At a minimum, client and server
 implementations MUST be capable of being configured to use HTTP Basic
 Authentication [RFC2617] in conjunction with a connection made with
 TLS 1.0 [RFC2246] or a subsequent standards-track version of TLS
 (such as [RFC4346]), supporting the conventions for using HTTP over
 TLS described in [RFC2818].

Gregorio & de hOra Standards Track [Page 36] RFC 5023 The Atom Publishing Protocol October 2007

 The choice of authentication mechanism will impact interoperability.
 The minimum level of security referenced above (Basic Authentication
 with TLS) is considered good practice for Internet applications at
 the time of publication of this specification and sufficient for
 establishing a baseline for interoperability.  Implementers are
 encouraged to investigate and use alternative mechanisms regarded as
 equivalently good or better at the time of deployment.  It is
 RECOMMENDED that clients be implemented in such a way that new
 authentication schemes can be deployed.
 Because this protocol uses HTTP response status codes as the primary
 means of reporting the result of a request, servers are advised to
 respond to unauthorized or unauthenticated requests using an
 appropriate 4xx HTTP response code (e.g., 401 "Unauthorized" or 403
 "Forbidden") in accordance with [RFC2617].

15. Security Considerations

 The Atom Publishing Protocol is based on HTTP and thus subject to the
 security considerations found in Section 15 of [RFC2616].
 The threats listed in this section apply to many protocols that run
 under HTTP.  The Atompub Working Group decided that the protection
 afforded by running authenticated HTTP under TLS (as described in
 Section 14) was sufficient to mitigate many of the problems presented
 by the attacks listed in this section.

15.1. Denial of Service

 Atom Publishing Protocol server implementations need to take adequate
 precautions to ensure malicious clients cannot consume excessive
 server resources (CPU, memory, disk, etc.).

15.2. Replay Attacks

 Atom Publishing Protocol server implementations are susceptible to
 replay attacks.  Specifically, this specification does not define a
 means of detecting duplicate requests.  Accidentally sent duplicate
 requests are indistinguishable from intentional and malicious replay
 attacks.

15.3. Spoofing Attacks

 Atom Publishing Protocol implementations are susceptible to a variety
 of spoofing attacks.  Malicious clients might send Atom Entries
 containing inaccurate information anywhere in the document.

Gregorio & de hOra Standards Track [Page 37] RFC 5023 The Atom Publishing Protocol October 2007

15.4. Linked Resources

 Atom Feed and Entry Documents can contain XML External Entities as
 defined in Section 4.2.2 of [REC-xml].  Atom implementations are not
 required to load external entities.  External entities are subject to
 the same security concerns as any network operation and can alter the
 semantics of an Atom document.  The same issues exist for Resources
 linked to by Atom elements such as atom:link and atom:content.

15.5. Digital Signatures and Encryption

 Atom Entry and Feed Documents can contain XML Digital Signatures
 [REC-xmldsig-core] and can be encrypted using XML Encryption
 [REC-xmlenc-core] as specified in Section 5 of [RFC4287].  Handling
 of signatures and encrypted elements in Atom documents is discussed
 in Sections 5 and 6.3 of [RFC4287].
 Neither servers nor clients are under any obligation to support
 encryption and digital signature of Entries or Feeds, although it is
 certainly possible that in some installations, clients or servers
 might require signing or encrypting of the documents exchanged in the
 Atom Protocol.
 Because servers are allowed (and in some cases, expected) to modify
 the contents of an Entry Document before publishing it, signatures
 within an entry are only likely to be useful to the server to which
 the entry is being sent.  Clients cannot assume that the signature
 will be valid when viewed by a third party, or even that the server
 will publish the client's signature.
 A server is allowed to strip client-applied signatures, to strip
 client-applied signatures and then re-sign with its own public key,
 and to oversign an entry with its own public key.  The meaning to a
 third party of a signature applied by a server is the same as a
 signature from anyone, as described in [RFC4287].  It is RECOMMENDED
 that a server that is aware that it has changed any part of an Entry
 Document that was signed by the client should strip that signature
 before publishing the entry in order to prevent third parties from
 trying to interpret a signature that cannot be validated.

15.6. URIs and IRIs

 Atom Publishing Protocol implementations handle URIs and IRIs.  See
 Section 7 of [RFC3986] and Section 8 of [RFC3987] for security
 considerations related to their handling and use.

Gregorio & de hOra Standards Track [Page 38] RFC 5023 The Atom Publishing Protocol October 2007

 The Atom Publishing Protocol leaves the server in control of minting
 URIs.  The use of any client-supplied data for creating new URIs is
 subject to the same concerns as described in the next section.

15.7. Code Injection and Cross Site Scripting

 Atom Feed and Entry Documents can contain a broad range of content
 types including code that might be executable in some contexts.
 Malicious clients could attempt to attack servers or other clients by
 injecting code into a Collection Document's Entry or Media Resources.
 Server implementations are strongly encouraged to verify that client-
 supplied content is safe prior to accepting, processing, or
 publishing it.  In the case of HTML, experience indicates that
 verification based on a white list of acceptable content is more
 effective than a black list of forbidden content.
 Additional information about XHTML and HTML content safety can be
 found in Section 8.1 of [RFC4287].

16. IANA Considerations

 This specification uses two new media types that conform to the
 registry mechanism described in [RFC4288], a new message header that
 conforms to the registry mechanism described in [RFC3864], and two
 new link relations that conform to the registry mechanism described
 in [RFC4287].

16.1. Content-Type Registration for 'application/atomcat+xml'

 An Atom Publishing Protocol Category Document, when serialized as XML
 1.0, can be identified with the following media type:
 MIME media type name:  application
 MIME subtype name:  atomcat+xml
 Required 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.

Gregorio & de hOra Standards Track [Page 39] RFC 5023 The Atom Publishing Protocol October 2007

 Security considerations:  As defined in RFC 5023.
    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:  RFC 5023.
 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:  .atomcat
 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 & email address to contact for further information:
    Joe Gregorio <joe@bitworking.org>
 Intended usage:  COMMON
 Author/Change controller:  IETF (iesg@ietf.org) Internet Engineering
    Task Force

16.2. Content-Type Registration for 'application/atomsvc+xml'

 An Atom Publishing Protocol Service Document, when serialized as XML
 1.0, can be identified with the following media type:
 MIME media type name:  application
 MIME subtype name:  atomsvc+xml
 Required parameters:  None.

Gregorio & de hOra Standards Track [Page 40] RFC 5023 The Atom Publishing Protocol October 2007

 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 RFC 5023.
    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:  RFC 5023.
 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:  .atomsvc
 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:  IETF (iesg@ietf.org) Internet Engineering
    Task Force

Gregorio & de hOra Standards Track [Page 41] RFC 5023 The Atom Publishing Protocol October 2007

16.3. Header Field Registration for 'SLUG'

 Header field name:  SLUG
 Applicable protocol:  http [RFC2616]
 Status:  standard.
 Author/Change controller:  IETF (iesg@ietf.org) Internet Engineering
    Task Force
 Specification document(s):  RFC 5023.
 Related information:  None.

16.4. The Link Relation Registration "edit"

 Attribute Value:  edit
 Description:  An IRI of an editable Member Entry.  When appearing
    within an atom:entry, the href IRI can be used to retrieve,
    update, and delete the Resource represented by that Entry.
 Expected display characteristics:  Undefined; this relation can be
    used for background processing or to provide extended
    functionality without displaying its value.
 Security considerations:  Automated agents should take care when this
    relation crosses administrative domains (e.g., the URI has a
    different authority than the current document).

16.5. The Link Relation Registration "edit-media"

 Attribute Value:  edit-media
 Description:  An IRI of an editable Media Resource.  When appearing
    within an atom:entry, the href IRI can be used to retrieve,
    update, and delete the Media Resource associated with that Entry.
 Expected display characteristics:  Undefined; this relation can be
    used for background processing or to provide extended
    functionality without displaying its value.
 Security considerations:  Automated agents should take care when this
    relation crosses administrative domains (e.g., the URI has a
    different authority than the current document).

Gregorio & de hOra Standards Track [Page 42] RFC 5023 The Atom Publishing Protocol October 2007

16.6. The Atom Format Media Type Parameter

 IANA has added a reference to this specification in the
 'application/atom+xml' media type registration.

17. References

17.1. Normative References

 [REC-xml]  Yergeau, F., Paoli, J., Bray, T., Sperberg-McQueen, C.,
            and E. Maler, "Extensible Markup Language (XML) 1.0
            (Fourth Edition)", World Wide Web Consortium
            Recommendation REC-xml-20060816, August 2006,
            <http://www.w3.org/TR/2006/REC-xml-20060816>.
 [REC-xml-infoset]
            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>.
 [REC-xml-names]
            Hollander, D., Bray, T., Tobin, R., and A. Layman,
            "Namespaces in XML 1.0 (Second Edition)", World Wide Web
            Consortium Recommendation REC-xml-names-20060816, August
            2006, <http://www.w3.org/TR/2006/REC-xml-names-20060816>.
 [REC-xmlbase]
            Marsh, J., "XML Base", W3C REC W3C.REC-xmlbase-20010627,
            June 2001,
            <http://www.w3.org/TR/2001/REC-xmlbase-20010627>.
 [REC-xmldsig-core]
            Solo, D., Reagle, J., and D. Eastlake, "XML-Signature
            Syntax and Processing", World Wide Web Consortium
            Recommendation REC-xmldsig-core-20020212, February 2002,
            <http://www.w3.org/TR/2002/REC-xmldsig-core-20020212>.
 [REC-xmlenc-core]
            Eastlake, D. and J. Reagle, "XML Encryption Syntax and
            Processing", World Wide Web Consortium Recommendation REC-
            xmlenc-core-20021210, December 2002,
            <http://www.w3.org/TR/2002/REC-xmlenc-core-20021210>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.

Gregorio & de hOra Standards Track [Page 43] RFC 5023 The Atom Publishing Protocol October 2007

 [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.
 [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
 [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
            Types", RFC 3023, January 2001.
 [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
            10646", STD 63, RFC 3629, November 2003.
 [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
            Procedures for Message Header Fields", BCP 90, RFC 3864,
            September 2004.
 [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.
 [RFC4287]  Nottingham, M. and R. Sayre, "The Atom Syndication
            Format", RFC 4287, December 2005.
 [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
            Registration Procedures", BCP 13, RFC 4288, December 2005.
 [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.1", RFC 4346, April 2006.

17.2. Informative References

 [NOTE-detect-lost-update]
            Nielsen, H. and D. LaLiberte, "Editing the Web: Detecting
            the Lost Update Problem Using Unreserved Checkout", World
            Wide Web Consortium NOTE NOTE-detect-lost-update, May
            1999, <http://www.w3.org/1999/04/Editing/>.

Gregorio & de hOra Standards Track [Page 44] RFC 5023 The Atom Publishing Protocol October 2007

 [REC-webarch]
            Walsh, N. and I. Jacobs, "Architecture of the World Wide
            Web, Volume One", W3C REC REC-webarch-20041215, December
            2004, <http://www.w3.org/TR/2004/REC-webarch-20041215>.
 [RNC]      Clark, J., "RELAX NG Compact Syntax", December 2001,
            <http://www.oasis-open.org/committees/relax-ng/
            compact-20021121.html>.

Gregorio & de hOra Standards Track [Page 45] RFC 5023 The Atom Publishing Protocol October 2007

Appendix A. Contributors

 The content and concepts within are a product of the Atom community
 and the Atompub Working Group.

Appendix B. RELAX NG Compact Schema

 This appendix is informative.
 The Relax NG schema explicitly excludes elements in the Atom Protocol
 namespace that are not defined in this revision of the specification.
 Requirements for Atom Protocol processors encountering such markup
 are given in Sections 6.2 and 6.3 of [RFC4287].
 The Schema for Service Documents:
 # -*- rnc -*- # RELAX NG Compact Syntax Grammar for the Atom Protocol
 namespace app = "http://www.w3.org/2007/app"
 namespace atom = "http://www.w3.org/2005/Atom"
 namespace xsd = "http://www.w3.org/2001/XMLSchema"
 namespace xhtml = "http://www.w3.org/1999/xhtml"
 namespace local = ""
 start = appService
 # common:attrs
 atomURI = text
 appCommonAttributes =
    attribute xml:base { atomURI }?,
    attribute xml:lang { atomLanguageTag  }?,
    attribute xml:space {"default"|"preserved"}?,
    undefinedAttribute*
 atomCommonAttributes = appCommonAttributes
 undefinedAttribute = attribute * - (xml:base | xml:space  | xml:lang
   | local:*) { text }
 atomLanguageTag = xsd:string {
    pattern = "([A-Za-z]{1,8}(-[A-Za-z0-9]{1,8})*)?"
 }

Gregorio & de hOra Standards Track [Page 46] RFC 5023 The Atom Publishing Protocol October 2007

 atomDateConstruct =
     appCommonAttributes,
     xsd:dateTime
 # app:service
 appService =
    element app:service {
       appCommonAttributes,
       ( appWorkspace+
         & extensionElement* )
    }
 # app:workspace
 appWorkspace =
    element app:workspace {
       appCommonAttributes,
       ( atomTitle
         & appCollection*
         & extensionSansTitleElement* )
    }
 atomTitle = element atom:title { atomTextConstruct }
 # app:collection
 appCollection =
    element app:collection {
       appCommonAttributes,
       attribute href { atomURI  },
       ( atomTitle
         & appAccept*
         & appCategories*
         & extensionSansTitleElement* )
    }
 # app:categories
 atomCategory =
     element atom:category {
        atomCommonAttributes,
        attribute term { text },
        attribute scheme { atomURI }?,
        attribute label { text }?,
        undefinedContent
     }

Gregorio & de hOra Standards Track [Page 47] RFC 5023 The Atom Publishing Protocol October 2007

 appInlineCategories =
     element app:categories {
         attribute fixed { "yes" | "no" }?,
         attribute scheme { atomURI }?,
         (atomCategory*,
         undefinedContent)
     }
 appOutOfLineCategories =
     element app:categories {
         attribute href { atomURI },
         undefinedContent
     }
 appCategories = appInlineCategories | appOutOfLineCategories
 # app:accept
 appAccept =
    element app:accept {
          appCommonAttributes,
          ( text? )
    }
 # Simple Extension
 simpleSansTitleExtensionElement =
    element * - (app:*|atom:title) {
       text
    }
 simpleExtensionElement =
    element * - (app:*) {
       text
    }
 # Structured Extension
 structuredSansTitleExtensionElement =
    element * - (app:*|atom:title) {
       (attribute * { text }+,
          (text|anyElement)*)
     | (attribute * { text }*,
        (text?, anyElement+, (text|anyElement)*))
    }

Gregorio & de hOra Standards Track [Page 48] RFC 5023 The Atom Publishing Protocol October 2007

 structuredExtensionElement =
    element * - (app:*) {
       (attribute * { text }+,
          (text|anyElement)*)
     | (attribute * { text }*,
        (text?, anyElement+, (text|anyElement)*))
    }
 # Other Extensibility
 extensionSansTitleElement =
  simpleSansTitleExtensionElement|structuredSansTitleExtensionElement
 extensionElement = simpleExtensionElement |
    structuredExtensionElement
 undefinedContent = (text|anyForeignElement)*
 # Extensions
 anyElement =
    element * {
       (attribute * { text }
        | text
        | anyElement)*
    }
 anyForeignElement =
     element * - app:* {
        (attribute * { text }
         | text
         | anyElement)*
     }
 atomPlainTextConstruct =
     atomCommonAttributes,
     attribute type { "text" | "html" }?,
     text
 atomXHTMLTextConstruct =
     atomCommonAttributes,
     attribute type { "xhtml" },
     xhtmlDiv
 atomTextConstruct = atomPlainTextConstruct | atomXHTMLTextConstruct

Gregorio & de hOra Standards Track [Page 49] RFC 5023 The Atom Publishing Protocol October 2007

 anyXHTML = element xhtml:* {
     (attribute * { text }
      | text
      | anyXHTML)*
 }
 xhtmlDiv = element xhtml:div {
   (attribute * { text }
    | text
    | anyXHTML)*
 }
 # EOF
 The Schema for Category Documents:
 # -*- rnc -*- # RELAX NG Compact Syntax Grammar for the Atom Protocol
 namespace app = "http://www.w3.org/2007/app"
 namespace atom = "http://www.w3.org/2005/Atom"
 namespace xsd = "http://www.w3.org/2001/XMLSchema"
 namespace local = ""
 start = appCategories
 atomCommonAttributes =
    attribute xml:base { atomURI }?,
    attribute xml:lang { atomLanguageTag }?,
    undefinedAttribute*
 undefinedAttribute = attribute * - (xml:base | xml:lang | local:*) {
   text }
 atomURI = text
 atomLanguageTag = xsd:string {
    pattern = "([A-Za-z]{1,8}(-[A-Za-z0-9]{1,8})*)?"
 }
 atomCategory =
     element atom:category {
        atomCommonAttributes,
        attribute term { text },
        attribute scheme { atomURI }?,
        attribute label { text }?,
        undefinedContent
     }

Gregorio & de hOra Standards Track [Page 50] RFC 5023 The Atom Publishing Protocol October 2007

 appInlineCategories =
     element app:categories {
         attribute fixed { "yes" | "no" }?,
         attribute scheme { atomURI }?,
         (atomCategory*,
         undefinedContent)
     }
 appOutOfLineCategories =
     element app:categories {
         attribute href { atomURI },
         (empty)
     }
 appCategories = appInlineCategories | appOutOfLineCategories
 # Extensibility
 undefinedContent = (text|anyForeignElement)*
 anyElement =
    element * {
       (attribute * { text }
        | text
        | anyElement)*
    }
 anyForeignElement =
     element * - atom:* {
        (attribute * { text }
         | text
         | anyElement)*
     }
 # EOF

Gregorio & de hOra Standards Track [Page 51] RFC 5023 The Atom Publishing Protocol October 2007

Authors' Addresses

 Joe Gregorio (editor)
 Google
 EMail: joe@bitworking.org
 URI:   http://bitworking.org/
 Bill de hOra (editor)
 NewBay Software
 EMail: bill@dehora.net
 URI:   http://dehora.net/

Gregorio & de hOra Standards Track [Page 52] RFC 5023 The Atom Publishing Protocol October 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
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Gregorio & de hOra Standards Track [Page 53]

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