Network Working Group J. Snell
Internet-Draft October 10, 2006
Expires: April 13, 2007
Atom Publishing Protocol Features Extension
draft-snell-atompub-feature-01.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document introduces extensions to the Atom Publishing Protocol
introspection format for expressing metadata about the features
supported by an Atom Publishing Protocol server implementation.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Feature Introspection and the 'f:feature' element . . . . . . . 3
3.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Publishing Controls and the 'f:control' element . . . . . . . . 5
4.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . . . 9
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1. Introduction
This document introduces extensions for the Atom Publishing Protocol
introspection format for expressing metadata about the features
supported by an Atom Publishing Protocol server implementation.
2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, [RFC2119].
This specification uses XML Namespaces [W3C.REC-xml-names-19990114]
to uniquely identify XML element names. It uses the following
namespace prefix for the indicated namespace URI;
"f": "http://purl.org/atompub/features/1.0"
This specification uses terms from the XML Infoset [W3C.REC-xml-
infoset-20040204]. However, this specification uses a shorthand; the
phrase "Information Item" is omitted when naming Element Information
Items. Therefore, when this specification uses the terms "element"
and "attribute" it is referring, respectively, to the Element and
Attribute Information Items in Infoset terms.
3. Feature Introspection and the 'f:feature' element
A feature is an abstract behavior, function and capability supported
by an Atom Publishing Protocol server. Examples of features that
might be supported by an APP server include support for a particular
set of Atom format extensions, a particular authentication scheme, or
a specific set of behaviors. The presence of a f:feature element in
an app:collection element is an indication that the collection
supports the feature and may require that a client wishing to use the
endpoint use that feature. Features are identified using permanent,
universally unique IRI's.
feature = element f:feature {
atomCommonAttributes,
attribute ref { atomUri },
attribute required { 'yes' | 'no' }?,
attribute href { atomURI }?,
attribute label { text }?,
(extensionElement*)
}
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The "ref" attribute specifies an IRI that uniquely identifies a
feature supported by a collection. The value of the ref attribute
MUST be compared on a case-sensitive, character-by-character basis.
Relative references MUST NOT be used.
A 'required' attribute value of "yes" indicates that clients MUST
utilize the identified feature when interacting with the collection.
A server MAY reject requests from clients that do not support or use
the feature. If not specified, the value is assumed to be "no".
An optional 'href' attribute MAY be used to specify the URI of a
human-readable description of the feature.
The optional 'label' attribute MAY be used to specify a human-
readable label for the feature. The value of the 'label' attribute
is Language-Sensitive as defined by Section 2 of [RFC4287].
The f:feature element MAY contain child elements and attributes other
than those defined in this specification. Such "foreign markup" are
considered to be metadata applicable to the feature identified by the
f:feature element. Software agents MUST NOT stop processing or
signal an error or change their behavior as a result of encountering
such foreign markup.
An app:collection element MAY contain zero or more f:feature elements
but MUST NOT contain more than one with the same ref attribute value.
The order in which f:feature elements appears is insignificant.
3.1. Example
The following is an example of a collection supporting one required
and one optional feature.
<service xmlns="...">
<workspace title="My Atom Service">
<collection title="My Atom Collection" href="...">
...
<f:feature ref="http://example.org/features/changetracking"
href="http://example.org/features/changetracking.html"
label="Change Tracking">
<rh:history xmlns:rh="..." href="revisionhistory.xml" />
</f:feature>
<f:feature ref="http://code.google.com/apis/gdata/"
href="http://code.google.com/apis/gdata/"
label="Google Data API"
required="yes" />
</collection>
</workspace>
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</app:server>
4. Publishing Controls and the 'f:control' element
Publishing Controls are a mechanism provided by the Atom Publishing
Protocol to embed metadata within atom:entry elements designed to
influence the way a server processes the entry. The pub:control
element is provided as a convenient container for this metadata
within an atom:entry. The Atom Publishing Protocol does not define a
mechanism by which clients can discover which publishing controls a
server supports.
The presence of a f:control element in an app:collection element is
an indication that the collection supports the control and may
require that a client wishing to use the endpoint use that control.
Controls are identified using permanent, universally unique IRI's.
control = element f:control {
atomCommonAttributes,
attribute ref { atomUri },
attribute required { 'yes' | 'no' }?,
attribute href { atomURI }?,
attribute label { text }?,
(extensionElement*)
}
The "ref" attribute specifies an IRI that uniquely identifies a
control supported by a collection. The value of the ref attribute
MUST be compared on a case-sensitive, character-by-character basis.
Relative references MUST NOT be used.
A 'required' attribute value of "yes" indicates that clients MUST
utilize the identified control when interacting with the collection.
A server MAY reject requests from clients that do not support or use
the control. If not specified, the value is assumed to be "no".
An optional 'href' attribute MAY be used to specify the URI of a
human-readable description of the control.
The optional 'label' attribute MAY be used to specify a human-
readable label for the control. The value of the 'label' attribute
is Language-Sensitive as defined by Section 2 of [RFC4287].
The f:control element MAY contain child elements and attributes other
than those defined in this specification. Such "foreign markup" are
considered to be metadata applicable to the control identified by the
f:control element. Software agents MUST NOT stop processing or
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signal an error or change their behavior as a result of encountering
such foreign markup.
An app:collection element MAY contain zero or more f:control elements
but MUST NOT contain more than one with the same ref attribute value.
The order in which f:control elements appear is insignificant.
4.1. Example
The following is an example of a collection supporting one required
and one optional control.
<service xmlns="...">
<workspace title="My Weblog">
<collection title="My Entries" href="...">
...
<f:control ref="http://purl.org/atom/app#draft"
required="yes" />
<f:control ref="http://example.org/transforms"
required="no">
<x:transforms xmlns:x="http://example.org/transforms">
<x:transform>markdown</x:transform>
<x:transform>wiki</x:transform>
<x:transform>line-breaks</x:transform>
<x:none>
</x:states>
</f:feature>
</collection>
</workspace>
</app:server>
An example atom:entry using the listed controls could appear as:
<entry xmlns="http://www.w3.org/2005/Atom">
...
<control xmlns="...">
<draft>yes</draft>
<f:transform>markdown</f:transform>
<f:transform>line-breaks</f:transform>
</control>
...
</entry>
5. Security Considerations
Specific features and controls supported by a collection may
introduce security considerations and concerns beyond those discussed
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by the Atom Publishing Protocol and Atom Syndication Format
specifications. Implementors must refer to the specifications and
description of each feature and control to determine the security
considerations relevant to each.
6. IANA Considerations
This specification does not specify any considerations for IANA.
7. References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
Syndication Format", RFC 4287, December 2005.
[W3C.REC-xml-infoset-20040204]
Cowan, J. and R. Tobin, "XML Information Set (Second
Edition)", World Wide Web Consortium Recommendation REC-
xml-infoset-20040204, February 2004,
<http://www.w3.org/TR/2004/REC-xml-infoset-20040204>.
[W3C.REC-xml-names-19990114]
Layman, A., Bray, T., and D. Hollander, "Namespaces in
XML", World Wide Web Consortium Recommendation REC-xml-
names-19990114, January 1999,
<http://www.w3.org/TR/1999/REC-xml-names-19990114>.
Appendix A. Acknowledgements
The author acknowledges the feedback from Elias Torres, Robert Yates,
David Johnson, Byrne Reese, Joe Gregorio and the other members of the
IETF Atom Publishing working group during the development of this
specification.
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Author's Address
James M Snell
Phone:
Email: jasnell@gmail.com
URI: http://snellspace.com
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