Network Working Group J. Gregorio, Ed.
Internet-Draft BitWorking, Inc
Expires: April 14, 2006 B. de hOra, Ed.
Propylon Ltd.
October 11, 2005
The Atom Publishing Protocol
draft-ietf-atompub-protocol-05.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This memo presents a protocol for using XML (Extensible Markup
Language) and HTTP (HyperText Transport Protocol) to edit content.
The Atom Publishing Protocol (APP) is an application-level protocol
for publishing and editing Web resources. The protocol at its core
is the HTTP transport of Atom-formatted representations. The Atom
format is documented in the Atom Syndication Format
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(draft-ietf-atompub-format-11.txt).
Editorial Note
To provide feedback on this Internet-Draft, join the atom-protocol
mailing list (http://www.imc.org/atom-protocol/index.html) [1].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. XML Namespace and Language . . . . . . . . . . . . . . . . . 5
3. Notational Conventions . . . . . . . . . . . . . . . . . . . 6
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 7
5. The Atom Publishing Protocol Model . . . . . . . . . . . . . 8
5.1 Collections . . . . . . . . . . . . . . . . . . . . . . . 8
5.2 Editable Resources . . . . . . . . . . . . . . . . . . . . 9
5.2.1 Read . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2.2 Update . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2.3 Delete . . . . . . . . . . . . . . . . . . . . . . . . 10
5.3 Capabilities Discovery . . . . . . . . . . . . . . . . . . 11
5.4 Listing . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.5 Success and Failure . . . . . . . . . . . . . . . . . . . 12
6. Atom Publishing Protocol Documents . . . . . . . . . . . . . 13
6.1 Use of xml:base xml:lang . . . . . . . . . . . . . . . . . 13
6.2 Collection Documents . . . . . . . . . . . . . . . . . . . 14
6.2.1 Element Definitions . . . . . . . . . . . . . . . . . 14
6.3 Introspection Documents . . . . . . . . . . . . . . . . . 16
6.3.1 Element Definitions . . . . . . . . . . . . . . . . . 17
7. Introspection Resource . . . . . . . . . . . . . . . . . . . 20
7.1 Discovery . . . . . . . . . . . . . . . . . . . . . . . . 20
8. Collection Resources . . . . . . . . . . . . . . . . . . . . 21
8.1 GET . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.2 POST . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.3 Title: Header . . . . . . . . . . . . . . . . . . . . . . 22
9. Entry Collections . . . . . . . . . . . . . . . . . . . . . 23
9.1 Editing Entry Resources . . . . . . . . . . . . . . . . . 23
9.2 Role of Atom Entry Elements During Editing . . . . . . . . 23
10. Generic Collections . . . . . . . . . . . . . . . . . . . . 25
10.1 Editing Generic Resources . . . . . . . . . . . . . . . 25
10.2 Title: Header . . . . . . . . . . . . . . . . . . . . . 25
11. List Resources . . . . . . . . . . . . . . . . . . . . . . . 26
11.1 URI Templates . . . . . . . . . . . . . . . . . . . . . 26
11.2 URI Template Parameters . . . . . . . . . . . . . . . . 27
11.2.1 \{index\} URI template variable . . . . . . . . . . 27
11.2.2 \{daterange\} URI template variable . . . . . . . . 27
11.2.3 Other URI Template parameters . . . . . . . . . . . 28
12. Atom Entry Extensions . . . . . . . . . . . . . . . . . . . 29
13. Securing the Atom Protocol . . . . . . . . . . . . . . . . . 30
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14. Security Considerations . . . . . . . . . . . . . . . . . . 31
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 32
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 35
16.1 Normative References . . . . . . . . . . . . . . . . . . 35
16.2 Informative References . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 37
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 38
B. Revision History . . . . . . . . . . . . . . . . . . . . . . 39
Intellectual Property and Copyright Statements . . . . . . . 41
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1. Introduction
The Atom Publishing Protocol is an application-level protocol for
publishing and editing Web resources using HTTP [RFC2616] and XML 1.0
[W3C.REC-xml-20040204].
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2. XML Namespace and Language
The XML Namespaces URI [W3C.REC-xml-names-19990114] for the XML data
format described in this specification is: http://purl.org/atom/app#
XML elements defined by this specification MAY have an xml:lang
attribute, whose content indicates the natural language for the
element (and its descendents). The language context is only
significant for elements and attributes declared to be "Language-
Sensitive" by this specification. Requirements regarding the content
and interpretation of xml:lang are specified in [W3C.REC-xml-
20040204], Section 2.12.
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3. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Some sections of this specification are illustrated with fragments of
a non-normative RELAX NG Compact schema [RNC]. However, the text of
this specification provides the definition of conformance.
This specification uses the namespace prefix "app:" for the Namespace
URI identified in Section 2 above. It uses the namespace prefix
"atom:" for the Namespace URI identified in [AtomFormat]. Note that
choices of namespace prefix are arbitrary and not semantically
significant.
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4. Terminology
For convenience, this protocol may be referred to as "Atom Protocol"
or "APP". This specification uses both internally.
URI/IRI - A Uniform Resource Identifier and Internationalized
Resource Identifier, respectively. These terms (and the distinction
between them) are defined in [RFC3986] and [RFC3987].
Resource - A network data object or service that can be identified
by a URI, as defined in [RFC2616].
Representation - An entity included with a request or response as
defined in [RFC2616].
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5. The Atom Publishing Protocol Model
The Atom Publishing Protocol is a subset of HTTP that is used to edit
resources on the web. The APP operates on collections of Web
resources. Collections are HTTP resources, as are the members of the
collection. Both Collections and collection member resources support
the same basic interactions. The patterns of interaction are based
on the common HTTP verbs.
o GET is used to retrieve a representation of a resource or perform
a read-only query.
o POST is used to create a new, dynamically-named resource, or to
provide a block of data to a data-handling process.
o PUT is used to update a known resource.
o DELETE is used to remove a resource.
5.1 Collections
The APP groups resources into "Collections", which are analogous to
folders or directories found in a file system. In the figure we have
member resources in a collection.
+-------------------------+
| Collection |
| |
| +----------------+ |
| | Member_A | |
| +----------------+ |
| |
| +----------------+ |
| | Member_B | |
| +----------------+ |
| |
| +----------------+ |
| | Member_C | |
| +----------------+ |
| |
| ... |
| |
| +----------------+ |
| | Member_Oldest | |
| +----------------+ |
| |
+-------------------------+
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To add a new member to a collection an appropriate representation is
POSTed to the URI of the collection resource. Here we show it being
added to the beginnng of the list. The ordering of the members of
collections is in terms of the time at which each resource was last
updated, which includes the act of creating the resource. The
ordering of collection members is covered in more detail in Section 8
and Section 11.
+-------------------------+
| Collection |
| |
POST | +----------------+ |
--------->| Member_New | |
| +----------------+ |
| |
| +----------------+ |
| | Member_A | |
| +----------------+ |
| |
| +----------------+ |
| | Member_B | |
| +----------------+ |
| |
| +----------------+ |
| | Member_C | |
| +----------------+ |
| |
| ... |
| |
| +----------------+ |
| | Member_Oldest | |
| +----------------+ |
| |
+-------------------------+
You'll note that up until now we haven't said what kinds of
representations we are expecting at each of the resources. There are
two kinds of collections, Entry and Generic. In Entry Collections
all the members MUST have representations as Atom Entries. For
further restrictions on Entry Collection see Section 9 The other type
of collection is a Generic Collection. Generic Collections make no
restriction on the representations of their member resources.
5.2 Editable Resources
All the members of a collection are Editable Resources. An Editable
resource is a resource whose available HTTP methods can be used to
retrieve, update and delete it.
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5.2.1 Read
To retrieve a representation of the resource, you send a GET to the
URI of the Editable Resource. Remember that for members of Entry
Collections, the served representation will be an Atom Entry.
Client Server
| |
| 1.) GET to Editable Resource URI |
|------------------------------------------>|
| |
| 2.) 200 OK |
|<------------------------------------------|
| |
1. The client sends a GET request to the member's URI.
2. The server responds with the representation of the resource.
5.2.2 Update
To update an Editable Resource the client will PUT an updated
representation to the URI of the resource.
Client Server
| |
| 1.) PUT to Editable Resource URI |
|------------------------------------------>|
| |
| 2.) 200 OK |
|<------------------------------------------|
1. The client PUTs an updated representation to the member's URI.
2. The server MAY respond with an updated representation of the
member's new state.
5.2.3 Delete
An Editable Resource is deleted by sending it DELETE. Note that this
also removes it from all the collections that it belonged to.
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Client Server
| |
| 1.) DELETE to Editable Resource URI |
|------------------------------------------>|
| |
| 2.) 200 Ok |
|<------------------------------------------|
| |
1. The client sends a DELETE request to the member's URI.
2. The server responds with successful status code.
5.3 Capabilities Discovery
Each collection resource responds to GET and can return a Collection
Document as it's representation. The Collection Document enumerates
the capabilities of each collection and the format is described in
Section 6.2.
Client Server
| |
| 1.) GET to Collection |
|------------------------------->|
| |
| 2.) Collection Document |
|<-------------------------------|
| |
1. The client sends a GET request to the Collection Resource.
2. The server responds with a Collection Document containing a
description of the capabilities of the collection. The content
of this document can vary based on aspects of the client request,
including, but not limited to, authentication credentials.
5.4 Listing
Clients can request a listing of the Collection's membership.
Listing the Editable Resources that are members of a collection is
done using one of the List Resources in the Introspection Document,
utilizing the 'app:uri-template' element. The List Resource returns
Atom Feed Documents with one Atom Entry for each member resource that
match the selection criteria. This is true whether the collection is
an Entry Collection or a Generic Collection. If an Entry Collection
is being interrogated, the entries returned by a list resource SHOULD
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NOT to be considered complete representations of the member
resources. See Section 11 and Section 12 for more details on the
extensions and constraints found on the entries returned from List
Resources.
Client Server
| |
| 1.) GET to List Resource |
|------------------------------->|
| |
| 2.) 200 OK, Atom Feed Doc |
|<-------------------------------|
| |
1. The client sends a GET request to the Collection's URI.
2. The server responds with an Atom Feed Document containing a full
or partial listing of the Collection's membership.
5.5 Success and Failure
HTTP defines different classes of response, which are used by the
Atom Protocol. HTTP status codes of the form 2xx signal that a
request was successful. HTTP status codes of the form 4xx or 5xx
signal that an error has occurred, and the request has failed.
Consult the HTTP specification [RFC2616] for more detailed
definitions of each status code.
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6. Atom Publishing Protocol Documents
This specification describes two kinds of Atom Publishing Protocol
Documents: Atom Collections Documents and Atom Introspection
Documents.
An Atom Collection Document is a representation of an Atom
collection, including metadata about the collection, and some or all
of the members associated with it. Its root is the app:collection
element.
An Atom Introspection Document represents one or more workspaces,
which describe server-defined groupings of collections. Its root is
the app:service element.
namespace app = "..." start = appCollection | appIntrospection
Both kinds of Atom Publishing Protocol Documents are specified in
terms of the XML Information Set, serialised as XML 1.0 ([W3C.REC-
xml-20040204]). Atom Publishing Protocol Documents MUST be well-
formed XML. This specification does not define a DTD for Atom
Protocol, and hence does not require them to be valid (in the sense
used by XML).
Atom Collection Documents are identified with the "application/
atomcoll+xml" media type.
Atom Introspection Documents are identified with the "application/
atomserv+xml" media type.
Atom allows the use of IRIs [RFC3987], as well as URIs [RFC3986].
Every URI is an IRI, so any URI can be used where an IRI is needed.
While IRIs must, for many protocols, be mapped to URIs prior to
dereferencing, they MUST NOT be so mapped for comparison when used in
atom:id. Section 3.1 of [RFC3987] describes how to map an IRI to a
URI when necessary.
6.1 Use of xml:base xml:lang
Any element defined by this specification MAY have an xml:base
attribute [W3C.REC-xmlbase-20010627]. When xml:base is used in an
Atom Publishing Protocol Document, it serves the function described
in section 5.1.1 of [RFC3986], establishing the base URI (or IRI) for
resolving any relative references found within the effective scope of
the xml:base attribute.
Any element defined by this specification MAY have an xml:lang
attribute, whose content indicates the natural language for the
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element and its descendents. The language context is only
significant for elements and attributes declared to be "Language-
Sensitive" by this specification. Requirements regarding the content
and interpretation of xml:lang are specified in XML 1.0 ([W3C.REC-
xml-20040204]), Section 2.12.
appCommonAttributes =
attribute xml:base { atomUri }?,
attribute xml:lang { atomLanguageTag }?,
undefinedAttribute*
6.2 Collection Documents
The Collection Document describes the capabilities of a Collection,
the types of Entries that it will support, the URI Templates it
supports.
The Collection Document has the media-type 'application/atomcoll+xml'
(see Section 15).
Here's an example document:
<?xml version="1.0" encoding='utf-8'?>
<app:collection xmlns:app="http://purl.org/atom/app#">
<app:member-type>entry</pub:member-type>
<app:uri-template>http://example.org/{index}</pub:uri-template>
<app:uri-template>http://example.org/{daterange}</pub:uri-template>
</app:collection>
This example says the Collection contains Atom Entry documents, and
that there are two means of selecting entries using what are called
'URI Templates'; one based on the collection's order, and another
based on dates. See Section 11.1 for more about URI Templates.
6.2.1 Element Definitions
6.2.1.1 The 'app:collection' Element
The app:collection is the document element of a Collection Document.
appCollection =
element app:collection {
appCommonAttributes,
( appMemberType+
appSearchTemplate
& anyElement* )
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}
This specification defines two child elements for app:collection:
o app:member-type: any number of elements listing the types of
Entries that the Collection may contain.
o app:uri-template: any number of URI Templates for a List Resource
(See Section 11).
6.2.1.2 The 'app:member-type' Element
The app:member-type element contains information elements about the
types of Entries that the Collection may contain.
appMember =
element app:member-type {
appCommonAttributes,
appTypeValue
}
The element content of an app:member-type MUST be a string that is
non-empty, and matches either the "isegment-nz-nc" or the "IRI"
production in [RFC3987]. Note that use of a relative reference other
than a simple name is not allowed. If a name is given,
implementations MUST consider the link relation type to be equivalent
to the same name registered within the IANA Registry of Member Types
(Section 15), and thus the IRI that would be obtained by appending
the value of the rel attribute to the string
"http://www.iana.org/assignments/entrytype/".
The content of an app:member-type specifies constraints on the
Entries that may appear in the Collection. The app:collection
element MAY have multiple app:member-type elements. An Entry POSTed
to a Collection MUST meet the constraints of at least one of the app:
member-type constraints. It MAY meet more than one, but the minimum
requirement is at least one.
This specification defines two initial values for app:member-type
IANA registry:
o "entry" - The Collection is an Entry Collection as defined in
Section 9.
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o "generic" - The Collection is a Generic Collection as defined in
Section 10.
6.2.1.3 The 'app:uri-template' Element
The element content of an app:uri-template is a URI Template for a
List Resource (See Section 11). Every List resource, whose URI is
determined by filling in the parameters in a URI Template, MUST
return an Atom feed document as its representation. This Atom feed
document MUST NOT contain entries which do not match the selection
criteria.
6.3 Introspection Documents
In order for authoring to commence, a client must first discover the
capabilities and locations of collections offered.
The Introspection Document describes "workspaces", which are server-
defined groupings of collections. There is no requirement that
servers support multiple workspaces, and a collection may appear in
more than one workspace.
The Introspection Document has the media-type 'application/
atomserv+xml', see Section 15
Here's an example document:
<?xml version="1.0" encoding='utf-8'?>
<app:service xmlns:app="http://purl.org/atom/app#">
<app:workspace title="Main Site" >
<app:collection contents="entries"
title="My Blog Entries"
href="http://example.org/reilly/feed" />
<app:collection contents="generic"
title="Documents"
href="http://example.org/reilly/pic" />
</app:workspace>
<app:workspace title="Side Bar Blog">
<app:collection contents="entries" title="Entries"
href="http://example.org/reilly/feed" />
<app:collection contents="http://example.net/booklist"
title="Books"
href="http://example.org/reilly/books" />
</app:workspace>
</app:service>
This example says there are two workspaces, each consisting of two
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collections. The first workspace is called 'Mail', and has two
collections, called 'My Blog Entries' and 'Documents' whose locations
are 'http://example.org/reilly/feed' and
'http://example.org/reilly/pic'. 'My Blog Entries' contains Atom
Entries and 'Documents' contains Generic Entries. The second
workspace is called 'Side Bar Blog' and also has two collections,
called 'Entries' and 'Books' whose locations are
'http://example.org/reilly/feed' and
'http://example.org/reilly/booklist'. 'Entries' contains Atom
Entries and 'Books' contains Generic Entries (since its contents
attribute is not present you MUST assume it is a Generic Collection).
6.3.1 Element Definitions
6.3.1.1 The 'app:service' Element
The "app:service" element is the document element of a Introspection
Document, acting as a container for service data associated with one
or more workspaces. An app:service elements MAY contain any number
of app:workspace elements.
appService =
element app:service {
appCommonAttributes,
( appWorkspace*
& anyElement* )
}
6.3.1.2 The 'app:workspace' Element
The 'workspace' element contains information elements about the
collections of resources available for editing. The app:workspace
elements MAY contain any number of app:collection elements.
appWorkspace =
element app:workspace {
appCommonAttributes,
attribute title { text },
( appCollection*
& anyElement* )
}
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6.3.1.2.1 The 'title' Attribute
The app:workspace element MUST contain a 'title' attribute, which
conveys a human-readable name for the workspace. This attribute is
Language-Sensitive.
6.3.1.3 The 'app:collection' Element
The 'app:collection' element describes collections and their member
resources.
appCollection =
element app:collection {
appCommonAttributes,
attribute title { text },
attribute href { text },
attribute contents { text },
anyElement*
}
6.3.1.3.1 The 'title' Attribute
The app:collection element MUST contain a 'title' attribute, whose
value conveys a human-readable name for the workspace. This
attribute is Language-Sensitive.
6.3.1.3.2 The 'href' Attribute
The app:collection element MUST contain an 'href' attribute, whose
value conveys the IRI of the collection.
6.3.1.3.3 The 'contents' Attribute
The app:collection element MAY contain a 'contents' attribute. The
'contents' attribute conveys the nature of a collection's member
resources. This specification defines two initial values for the
'contents' attribute:
o 'entry': A value of 'entry' for the contents attribute indicates
that the Collection is an Entry Collection (Section 9).
o 'generic': A value of 'generic' for the contents attribute
indicates that the Collection is a Generic Collection
(Section 10).
If the attribute is not present, its value MUST be considered to be
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'generic'.
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7. Introspection Resource
To retrieve an Introspection Document, the client sends a GET request
to its URI.
GET /service-desc HTTP/1.1
Host: example.org
User-Agent: Cosimo/1.0
Accept: application/atomserv+xml
The server responds to a GET request by returning an Introspection
Document in the message body.
HTTP/1.1 200 OK
Date: Mon, 21 Mar 2005 19:20:19 GMT
Server: CountBasic/2.0
Last-Modified: Mon, 21 Mar 2005 19:17:26 GMT
ETag: "4c083-268-423f1dc6"
Content-Length: nnnn
Content-Type: application/atomserv+xml
<?xml version="1.0" encoding='utf-8'?>
<app:service xmlns:app="http://purl.org/atom/app#">
...
</app:service>
7.1 Discovery
[[anchor18: Add in desc of an HTML link element that points to the
Introspection Resource, or add it to the autodisco draft]]
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8. Collection Resources
An Atom Collection is a set of related resources. All members of a
collection have an "app:updated" property, and the Collection is
considered to be ordered by this property.
This specification defines two HTTP methods for use with collection
resources: GET and POST.
8.1 GET
A GET to a Collection Resource returns a Collection Document,
outlining the Collection. Collection Documents are described in
Section 6.2.
8.2 POST
In addition to GET, a Collection Resource also accepts POST requests.
The client POSTs a representation of the desired resource to the
Collection Resource. Note that some collections may impose
constraints on the media-types that are created in a Collection and
MAY generate a response with a status code of 415 ("Unsupported Media
Type").
In the case of a successful creation, the status code MUST be 201
("Created").
Every successful POST MUST return a Location: header with the URI of
the newly created resource.
Here's an example. Below, the client requests to create a resource
in a Collection:
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POST /edit HTTP/1.1
Host: example.org
User-Agent: Cosimo/1.0
Accept: application/atom+xml
Content-Type: application/atom+xml
Content-Length: 601
<atom:entry xmlns:atom="http://www.w3.org/2005/Atom">
<atom:title>Mars Attacks!</atom:title>
<atom:summary type="html">
Why cant we all just... get along?
</atom:summary>
<atom:author>
<atom:name>The President</atom:name>
<atom:uri>http://www.example.org/blog</atom:uri>
</atom:author>
<atom:content type="html" xml:lang="en"
xml:base="http://www.example.org/blog/">
<p>
Why can't we...work out our differences?
Why can't we...work things out?
Little people...why can't we all just...get along?
</p>
</atom:content>
</atom:entry>
The resource is created by sending an Atom Entry as the entity body.
Assuming the server created the resource successfully, it sends back
a 201 Created response with a Location: header that contains the IRI
of the newly created member as an Editable Resource.
HTTP/1.1 201 Created
Date: Fri, 7 Oct 2005 17:17:11 GMT
Content-Length: 663
Content-Type: application/atom+xml; charset="utf-8"
Location: http://example.org/edit/first-post.atom
8.3 Title: Header
The POST to a Collection Resource MAY contain a Title: header that
indicates the clients suggested name for the resource. The server
MAY ignore the Title: header or modify the requested name to suit
local conventions.
Title = "Title" ":" [text]
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9. Entry Collections
Entry Collections are Collections that restrict their membership to
Atom entries.
9.1 Editing Entry Resources
Atom entries are edited by sending HTTP requests to an individual
entry's URI. Servers can determine the processing necessary to
interpret a request by examining the request's HTTP method and
'Content-Type' header.
Processing Client Requests
+-----------+------+--------+--------+------+
| | GET | PUT | DELETE | POST |
+-----------+------+--------+--------+------+
| No Body | Read | x | Delete | x |
| | | | | |
| Atom Body | x | Update | x | x |
+-----------+------+--------+--------+------+
9.2 Role of Atom Entry Elements During Editing
The elements of an Atom Entry Document are either a 'Writable
Element' or a 'Round Trip Element'.
Writable Element - An element of an Atom Entry whose value is
editable by the client and not enforced by the server.
Round Trip Element - An element of an Atom Entry whose value is
enforced by the server and not editable by the client.
That categorization will determine the elements' disposition during
editing.
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+--------------------+------------+
| Atom Entry Element | Property |
+--------------------+------------+
| atom:author | Writable |
| | |
| atom:category | Writable |
| | |
| atom:content | Writable |
| | |
| atom:contributor | Writable |
| | |
| atom:id | Round Trip |
| | |
| atom:link | Writable |
| | |
| atom:published | Writable |
| | |
| atom:source | Writable |
| | |
| atom:summary | Writable |
| | |
| atom:title | Writable |
| | |
| atom:updated | Round Trip |
+--------------------+------------+
Table 2
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10. Generic Collections
Generic Collections are Collections that do not have uniform
restrictions on the representations of the member resources.
10.1 Editing Generic Resources
Member resources are edited by sending HTTP requests to an individual
resource's URI. Servers can determine the processing necessary to
interpret a request by examining the request's HTTP method and
'Content-Type' header.
Processing Client Requests
+----------+------+--------+--------+------+
| | GET | PUT | DELETE | POST |
+----------+------+--------+--------+------+
| No Body | Read | x | Delete | x |
| | | | | |
| Any Body | x | Update | x | x |
+----------+------+--------+--------+------+
When a List resource returns an Atom Feed enumerating the contents of
a Generic Collection, all the Entries MUST have an atom:content
element with a 'src' attribute.
10.2 Title: Header
The POST to a Generic Collection Resource MAY contain a Title: header
that indicates the clients suggested title for the resource. The
server MAY ignore the Title: header or modify the requested title to
suit local conventions.
Title = "Title" ":" [text]
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11. List Resources
List resources are resources which are identified by URI templates
indicating selection criteria. They can be used where clients
require fine control over the range or size of a server's response.
A list resource MUST return an Atom feed document as its
representation. The entries in the returned document MUST be ordered
by their 'atom:updated' property, with the most recently updated
entries coming first in the document order. Clients MUST NOT assume
that the entry returned in the feed is a full representation of a
member resource. If the entry is an Editable Resource then the
client should perform a GET on the member resource before editing.
note: in this section some URIs carry across onto the next line; this
is indicated by a '\'
11.1 URI Templates
URI Templates are a mechanism for declaring criteria against a list
resource. By itself a URI Template is not a valid URI. Instead
there are multiple parameters embedded in the URI and distinguished
by closing braces which can be populated and used as selection
criteria. The value of each app:uri-template element in a Collection
document is a URI Template.
Each URI template has one or more parameters that MUST be substituted
with values to construct a valid URI. The substitution MUST ensure
that the resulting value is also properly percent-encoded utf-8.
Here are some examples of template URIs and corresponding populated
values:
http://example.org/blog/edit/{index}
http://example.org/blog/edit/3-9
http://example.org/blog/edit/{index}/foo
http://example.org/blog/edit/0-100/foo
http://example.org/blog/edit/{daterange}
http://example.org/blog/edit/daterange=\
2003-12-13T18:30:02Z-2003-12-13T18:30:02Z
http://example.org/blog/edit?dr={daterange}/bar/
http://example.org/blog/edit?dr=\
2003-12-13T18:30:02Z,2003-12-13T18:30:02Z/bar/
Note that the parameters MAY appear at any place in the URI template.
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11.2 URI Template Parameters
This specification defines two parameters for use in URI Templates:
o index: allows selection into a collection's resources based as
though ordered by their 'atom:updated' property.
o daterange: allows selection into a collection's resources based on
their 'atom:updated' property
In both cases, the response to the selection request MUST be an Atom
Feed where all the entries fall within the requested criteria. The
request range is considered a closed set - if an entry matches one
end of the range exactly it MUST be included in the response. If no
members fall in the requested range, the server MUST respond with an
Atom Feed containing no entries.
A Collection Document MUST contain at least two app:uri-template
elements - one for the {index} parameter template and the other for
the {daterange} parameter template. The two parameters are not
mutually exclusive and MAY appear together in a single Template URI.
11.2.1 \{index\} URI template variable
The value of the {index} criterion MUST be a pair of non-negative
integer indices separated by a dash character. One or other index
MAY omitted, in which case the range is understood as stretching to
zero, or infinity.
index-specifier = [index] "-" [index]
For example, suppose the client is supplied this {index} URI
template:
http://example.org/blog/edit/{index}
If the client wants the first 15 entries in the Collection it would
substitute the brace-delimited parameter {index}, with the value
1-15, giving:
http://example.org/blog/edit/1-15
11.2.2 \{daterange\} URI template variable
A URI Template with the variable 'daterange' allows querying for Atom
Entries in a Collection according to their 'atom:updated' property.
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The value of the {daterange} criterion should be a pair of ISO
formatted dates separated by a dash character; either index may be
optionally omitted, in which case the range is understood as
stretching to infinity on that end.
daterange-specifier = [iso-date] "," [iso-date]
The [iso-date] terminal MUST conform to the "date-time" production in
[RFC3339]. In addition, an uppercase "T" character MUST be used to
separate date and time, and an uppercase "Z" character MUST be
present in the absence of a numeric time zone offset.
For example, suppose the client is supplied this {daterange} URI
Template:
http://example.org/blog/edit/{daterange}
If the client wants the entries in the collection between January and
February 2006 it would substitute the brace-delimited parameter
{daterange} with the desired selection value, giving this URI:
http://example.org/blog/edit/2006-01-01T00:00:00Z,\
2006-02-01T00:00:00Z
11.2.3 Other URI Template parameters
Other specifications MAY define new parameters for use in URI
templates and declared in the app:uri-template element.
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12. Atom Entry Extensions
This specification adds three new values to the Registry of Link
Relations.
The value of 'collection' signifies that the IRI in the value of the
href is the Collection that this Entry belongs to. Any entry MAY
contain a link with a relation of 'collection'.
The value of 'edit' signifies that the IRI in the value of the href
attribute identifies the resource that is used to edit the entry.
That is, it is the URI of the Entry as an Editable Resource.
The value of 'srcedit' signifies that the IRI in the value of the
href attribute identifies the resource that is used to edit the
resource pointed to by the 'src' attribute of the atom:content
element. That is, it is the IRI of the atom:content@src as an
Editable Resource. If a link element with a relation of "srcedit" is
not given, then it's value defaults to the "src" attribute of the
content element. List Resources for Generic Collections MUST return
entries that have 'srcedit' links or MUST have a atom:content@src
value.
If the "srcedit" link is present, and it's value is an empty string,
then there is no URI that can be treated in the way such a value
would be treated.
Clients SHOULD use the "srcedit" value to manipulate the resource
within the context of the APP itself. Clients SHOULD prefer the
"atom:content@src" value in any other context. For example, if the
resource is an image, a client may replace the image data using a PUT
on the "srcedit" value, and may even display a preview of the image
by fetching the "srcedit" URI. But when creating a public, read-only
reference to the same image resource, the client should use the
"atom:content@src" value.
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13. Securing the Atom Protocol
All instances of publishing Atom entries SHOULD be protected by
authentication to prevent posting or editing by unknown sources.
Atom servers and clients MUST support one of the following
authentication mechanisms, and SHOULD support both.
o HTTP Digest Authentication [RFC2617]
o [@@TBD@@ CGI Authentication ref]
Atom servers and clients MAY support encryption of the Atom session
using TLS [RFC2246].
There are cases where an authentication mechanism may not be
required, such as a publicly editable Wiki, or when using the PostURI
to post comments to a site that does not require authentication to
create comments.
13.1 [@@TBD@@ CGI Authentication]
This authentication method is included as part of the protocol to
allow Atom servers and clients that cannot use HTTP Digest
Authentication but where the user can both insert its own HTTP
headers and create a CGI program to authenticate entries to the
server. This scenario is common in environments where the user
cannot control what services the server employs, but the user can
write their own HTTP services.
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14. Security Considerations
Because Atom is a publishing protocol, it is important that only
authorized users can create and edit entries.
The security of Atom is based on HTTP Digest Authentication and/or
[@@TBD@@ CGI Authentication]. Any weaknesses in either of these
authentication schemes will affect the security of the Atom
Publishing Protocol.
Both HTTP Digest Authentication and [@@TBD@@ CGI Authentication] are
susceptible to dictionary-based attacks on the shared secret. If the
shared secret is a password (instead of a random string with
sufficient entropy), an attacker can determine the secret by
exhaustively comparing the authenticating string with hashed results
of the public string and dictionary entries.
See RFC 2617 for more detailed description of the security properties
of HTTP Digest Authentication.
@@TBD@@ Talk here about using HTTP basic and digest authentication.
@@TBD@@ Talk here about denial of service attacks using large XML
files, or the billion laughs DTD attack.
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15. IANA Considerations
A Atom Collection Document, when serialized as XML 1.0, can be
identified with the following media type:
MIME media type name: application
MIME subtype name: atomcoll+xml
Mandatory parameters: None.
Optional parameters:
"charset": This parameter has identical semantics to the charset
parameter of the "application/xml" media type as specified in
[RFC3023].
Encoding considerations: Identical to those of "application/xml" as
described in [RFC3023], section 3.2.
Security considerations: As defined in this specification.
[[anchor31: update upon publication]]
In addition, as this media type uses the "+xml" convention, it
shares the same security considerations as described in [RFC3023],
section 10.
Interoperability considerations: There are no known interoperability
issues.
Published specification: This specification. [[anchor32: update upon
publication]]
Applications that use this media type: No known applications
currently use this media type.
Additional information:
Magic number(s): As specified for "application/xml" in [RFC3023],
section 3.2.
File extension: .atomcoll
Fragment identifiers: As specified for "application/xml" in
[RFC3023], section 5.
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Base URI: As specified in [RFC3023], section 6.
Macintosh File Type code: TEXT
Person and email address to contact for further information: Joe
Gregorio <joe@bitworking.org>
Intended usage: COMMON
Author/Change controller: IESG
An Atom Introspection Document, when serialized as XML 1.0, can be
identified with the following media type:
MIME media type name: application
MIME subtype name: atomserv+xml
Mandatory parameters: None.
Optional parameters:
"charset": This parameter has identical semantics to the charset
parameter of the "application/xml" media type as specified in
[RFC3023].
Encoding considerations: Identical to those of "application/xml" as
described in [RFC3023], section 3.2.
Security considerations: As defined in this specification.
[[anchor33: update upon publication]]
In addition, as this media type uses the "+xml" convention, it
shares the same security considerations as described in [RFC3023],
section 10.
Interoperability considerations: There are no known interoperability
issues.
Published specification: This specification. [[anchor34: update upon
publication]]
Applications that use this media type: No known applications
currently use this media type.
Additional information:
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Magic number(s): As specified for "application/xml" in [RFC3023],
section 3.2.
File extension: .atomsrv
Fragment identifiers: As specified for "application/xml" in
[RFC3023], section 5.
Base URI: As specified in [RFC3023], section 6.
Macintosh File Type code: TEXT
Person and email address to contact for further information: Joe
Gregorio <joe@bitworking.org>
Intended usage: COMMON
Author/Change controller: This specification's author(s). [[anchor35:
update upon publication]]
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16. References
16.1 Normative References
[AtomFormat]
Nottingham, M. and R. Sayre, "The Atom Syndication
Format", 1.0, July 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, July 2002.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[W3C.REC-xml-20040204]
Yergeau, F., Paoli, J., Sperberg-McQueen, C., Bray, T.,
and E. Maler, "Extensible Markup Language (XML) 1.0 (Third
Edition)", W3C REC REC-xml-20040204, February 2004.
[W3C.REC-xml-names-19990114]
Hollander, D., Bray, T., and A. Layman, "Namespaces in
XML", W3C REC REC-xml-names-19990114, January 1999.
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16.2 Informative References
[RNC] Clark, J., "RELAX NG Compact Syntax", December 2001.
[W3C.REC-webarch-20041215]
Walsh, N. and I. Jacobs, "Architecture of the World Wide
Web, Volume One", W3C REC REC-webarch-20041215,
December 2004.
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URIs
[1] <http://www.imc.org/atom-protocol/index.html>
Authors' Addresses
Joe Gregorio (editor)
BitWorking, Inc
1002 Heathwood Dairy Rd.
Apex, NC 27502
US
Phone: +1 919 272 3764
Email: joe@bitworking.com
URI: http://bitworking.com/
Bill de hOra (editor)
Propylon Ltd.
45 Blackbourne Square, Rathfarnham Gate
Dublin, Dublin D14
IE
Phone: +353-1-4927444
Email: bill.dehora@propylon.com
URI: http://www.propylon.com/
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Appendix A. Contributors
The content and concepts within are a product of the Atom community
and the Atompub Working Group. Robert Sayre was an editor for drafts
00-04.
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Appendix B. Revision History
draft-ietf-atompub-protocol-05 - Added: Contributors section. Added:
de hOra to editors. Fixed: typos. Added diagrams and description to
model section. Incorporates PaceAppDocuments, PaceAppDocuments2,
PaceSimplifyCollections2 (large-sized chunks of it anyhow: the
notions of Entry and Generic resources, the section 4 language on the
Protocol Model, 4.1 through 4.5.2, the notion of a Collection
document, as in Section 5 through 5.3, Section 7 "Collection
resources", Selection resources (modified from pace which talked
about search); results in major mods to Collection Documents, Section
9.2 "Title: Header" and brokeout para to section 9.1 Editing Generic
Resources). Added XML namespace and language section. Some cleanup
of front matter. Added Language Sensitivity to some attributes.
Removed resource descriptions from terminology. Some juggling of
sections. See:
http://www.imc.org/atom-protocol/mail-archive/msg01812.html.
draft-ietf-atompub-protocol-04 - Add ladder diagrams, reorganize, add
SOAP interactions
draft-ietf-atompub-protocol-03 - Incorporates PaceSliceAndDice3 and
PaceIntrospection.
draft-ietf-atompub-protocol-02 - Incorporates Pace409Response,
PacePostLocationMust, and PaceSimpleResourcePosting.
draft-ietf-atompub-protocol-01 - Added in sections on Responses for
the EditURI. Allow 2xx for response to EditURI PUTs. Elided all
mentions of WSSE. Started adding in some normative references.
Added the section "Securing the Atom Protocol". Clarified that it is
possible that the PostURI and FeedURI could be the same URI. Cleaned
up descriptions for Response codes 400 and 500.
Rev draft-ietf-atompub-protocol-00 - 5Jul2004 - Renamed the file and
re-titled the document to conform to IETF submission guidelines.
Changed MIME type to match the one selected for the Atom format.
Numerous typographical fixes. We used to have two 'Introduction'
sections. One of them was moved into the Abstract the other absorbed
the Scope section. IPR and copyright notifications were added.
Rev 09 - 10Dec2003 - Added the section on SOAP enabled clients and
servers.
Rev 08 - 01Dec2003 - Refactored the specification, merging the
Introspection file into the feed format. Also dropped the
distinction between the type of URI used to create new entries and
the kind used to create comments. Dropped user preferences.
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Rev 07 - 06Aug2003 - Removed the use of the RSD file for auto-
discovery. Changed copyright until a final standards body is chosen.
Changed query parameters for the search facet to all begin with atom-
to avoid name collisions. Updated all the Entries to follow the 0.2
version. Changed the format of the search results and template file
to a pure element based syntax.
Rev 06 - 24Jul2003 - Moved to PUT for updating Entries. Changed all
the mime-types to application/x.atom+xml. Added template editing.
Changed 'edit-entry' to 'create-entry' in the Introspection file to
more accurately reflect it's purpose.
Rev 05 - 17Jul2003 - Renamed everything Echo into Atom. Added
version numbers in the Revision history. Changed all the mime-types
to application/atom+xml.
Rev 04 - 15Jul2003 - Updated the RSD version used from 0.7 to 1.0.
Change the method of deleting an Entry from POSTing <delete/> to
using the HTTP DELETE verb. Also changed the query interface to GET
instead of POST. Moved Introspection Discovery to be up under
Introspection. Introduced the term 'facet' for the services listed
in the Introspection file.
Rev 03 - 10Jul2003 - Added a link to the Wiki near the front of the
document. Added a section on finding an Entry. Retrieving an Entry
now broken out into it's own section. Changed the HTTP status code
for a successful editing of an Entry to 205.
Rev 02 - 7Jul2003 - Entries are no longer returned from POSTs,
instead they are retrieved via GET. Cleaned up figure titles, as
they are rendered poorly in HTML. All content-types have been
changed to application/atom+xml.
Rev 01 - 5Jul2003 - Renamed from EchoAPI.html to follow the more
commonly used format: draft-gregorio-NN.html. Renamed all references
to URL to URI. Broke out introspection into it's own section. Added
the Revision History section. Added more to the warning that the
example URIs are not normative.
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Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
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Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Gregorio & de hOra Expires April 14, 2006 [Page 42]
