Network Working Group J. Snell
Internet-Draft October 27, 2007
Intended status: Experimental
Expires: April 29, 2008
Atom Publishing Protocol Feature Discovery
draft-snell-atompub-feature-12.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document introduces extensions to the Atom Publishing Protocol
Service Document format for expressing metadata about the behaviors,
functions and capabilities supported by an Atom Publishing Protocol
collection.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. The f:features Element . . . . . . . . . . . . . . . . . . . . 4
4. The f:feature element . . . . . . . . . . . . . . . . . . . . 5
4.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Feature Documents . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. The "supportsDraft" Feature . . . . . . . . . . . . . . . . . 7
7. The "ignoresDraft" Feature . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9.1. Content-type registration for
'application/atomfeature+xml' . . . . . . . . . . . . . . 8
10. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
This document introduces an extension to the Atom Publishing Protocol
(Atompub) service document [RFC5023] format that allows for the
documentation and discovery of behaviors, functions or capabilities
supported by an Atompub collection. Examples of such capabilities
can include the preservation of certain kinds of content, support for
draft entries, support for the scheduled publication of entries, use
of a particular set of Atom format extensions, and so on.
Describing features using the mechanisms defined in this
specification is currently considered to be largely experimental.
While there are examples of such mechanisms being put to practical
use in deployed applications, there is currently not enough
collective implementation experience to determine whether the
mechanism defined here is sufficient to fully address the general
needs of Atom Publishing Protocol client and server implementations.
Implementations and feedback are encouraged.
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-20060816]
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.
This specification uses the terms "atomUri" and
"atomCommonAttributes" from the non-normative RELAX NG Compact schema
included in [RFC4287]. Where used, these serve the same purpose and
have the same meaning as their use in [RFC4287].
Atom allows the use of IRIs [RFC3987]. Every URI [RFC3986] is also
an IRI, so a URI may be used wherever below an IRI is named. There
are two special considerations: (1) when an IRI that is not also a
URI is given for dereferencing, it MUST be mapped to a URI using the
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steps in Section 3.1 of [RFC3987] and (2) when an IRI is serving as
an identifier, it MUST NOT be so mapped.
Any element defined by this specification MAY have an xml:base
attribute [W3C.REC-xmlbase-20010627]. When xml:base is used, 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
element and its descendents. The language context is only
significant for elements and attributes declared to be "Language-
Sensitive". Requirements regarding the content and interpretation of
xml:lang are specified in XML 1.0 [W3C.REC-xml-20060816], Section
2.12.
3. The f:features Element
The f:features element is used in an app:collection element or as the
root element of a Features Document as a container for zero or more
f:feature elements.
An f:features element MAY contain any number of f:feature elements
but MUST NOT contain more than one with the same ref attribute value.
The order in which f:feature elements appear within the f:features
element is insignificant.
An app:collection element MUST NOT contain more than one f:features
element.
inlineFeatures =
element f:features {
(feature*,
undefinedContent)
}
outOfLineFeatures =
element f:features {
attribute href { atomURI }
}
features = inlineFeatures | outOfLineFeatures
When used within an app:collection element, the f:features element
MAY contain an "href" attribute, whose value MUST be an IRI reference
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identifying a Features Document. If the "href" attribute is
provided, the f:features element MUST be empty.
4. The f:feature element
The f:feature element is used within an f:features element to declare
a collection's support for a feature.
feature = element f:feature {
atomCommonAttributes,
attribute ref { atomUri },
attribute href { atomUri }?,
attribute label { text }?,
(anyElement)*
}
anyElement = element * - f:feature {
(attribute * { text }
| text
| anyElement)*
}
The ref attribute specifies a globally unique IRI identifying a
feature. The value of the ref attribute MUST be compared on a case-
sensitive, character-by-character basis. Relative references MUST
NOT be used. The IRI is used strictly for identification and cannot
be assumed to be dereferenceable.
An optional href attribute MAY be used to specify a dereferenceable
IRI of a human-readable description of the feature. Relative
references MAY be used.
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 a mix of text and any number of
child elements and attributes from any XML namespace, with the
exception of the f:feature element itself. Such markup is considered
to be metadata applicable to the feature identified. Software agents
MUST NOT stop processing or signal an error or change their behavior
as a result of encountering such markup.
The presence of a f:feature element is an indication that the
collection supports the feature identified. The lack of a f:feature
element identifying a particular feature indicates that support for
that feature is unspecified. This does not mean that the feature is
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not supported, only that the server has not explicitly declared
support. There are no means by which a server can indicate that a
given feature is unsupported.
4.1. Example
The following is an example of a collection using the f:feature
element to indicate its support for the app:draft element as defined
by [RFC5023].
My Workspace
My Atom Collection
application/atom+xml;type=entry
5. Feature Documents
A Feature Document contains a listing of f:feature elements that can
be referenced by multiple app:collection elements. Separating the
list of f:features out into a separate document enables and promotes
the reuse of features across multiple collections.
The root of a Feature Document is the f:features element. The
f:features element MUST NOT contain an href atribute. Feature
documents are identified with the "application/atomfeature+xml" media
type (see Section 9.1).
5.1. Example
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This Feature Document indicates support for the app:draft publishing
control and a hypothetical extension.
The following is an example of a collection using the f:features
element to reference a Feature Document.
My Workspace
My Atom Collection
application/atom+xml;type=entry
6. The "supportsDraft" Feature
The "supportsDraft" feature is used to indicate that a collection
supports the use of the app:draft control element as defined by
Section 13.1.1 of [RFC5023]. The IRI of the "supportsDraft" feature
is:
http://purl.org/atompub/features/1.0/supportsDraft
7. The "ignoresDraft" Feature
The "ignoresDraft" feature is used to indicate that a collection will
ignore the use of the app:draft control element as defined by Section
13.1.1 of [RFC5023]. The IRI of the "ignoresDraft" feature is:
http://purl.org/atompub/features/1.0/ignoresDraft
A server MUST NOT declare support for both the "supportsDraft" and
"ignoresDraft" features within the a single app:collection element.
8. Security Considerations
Specific features supported by a collection may introduce security
considerations and concerns beyond those discussed by the Atom
Publishing Protocol and Atom Syndication Format specifications.
Implementors must refer to the specifications and description of each
feature to determine the security considerations relevant to each.
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Implementations of this specification handle URIs and IRIs. See
Section 7 of [RFC3986] and Section 8 of [RFC3987] for security
considerations related to their handling and use.
9. IANA Considerations
This specification uses a new media type that conforms to the
registry mechanism described in [RFC4288].
9.1. Content-type registration for 'application/atomfeature+xml'
A Feature Document, when serialized as XML 1.0, can be identified
with the following media type:
MIME media type name: application
MIME subtype name: atomfeature+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.
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.
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: .atomfeature
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: James
Snell
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Intended usage: COMMON
Author/Change controller: IETF (iesg@ietf.org) Internet Engineering
Task Force
10. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[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., Ed. and R. Sayre, Ed., "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.
[RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing
Protocol", RFC 5023, October 2007.
[W3C.REC-xml-20060816]
Paoli, J., Maler, E., Yergeau, F., Bray, T., and C.
Sperberg-McQueen, "Extensible Markup Language (XML) 1.0
(Fourth Edition)", World Wide Web Consortium
Recommendation REC-xml-20060816, August 2006,
.
[W3C.REC-xml-infoset-20040204]
Tobin, R. and J. Cowan, "XML Information Set (Second
Edition)", World Wide Web Consortium Recommendation REC-
xml-infoset-20040204, February 2004,
.
[W3C.REC-xml-names-20060816]
Hollander, D., Tobin, R., Bray, T., and A. Layman,
"Namespaces in XML 1.0 (Second Edition)", World Wide Web
Consortium Recommendation REC-xml-names-20060816,
August 2006,
.
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[W3C.REC-xmlbase-20010627]
Marsh, J., "XML Base", World Wide Web Consortium
Recommendation REC-xmlbase-20010627, June 2001,
.
Appendix A. Acknowledgements
The author acknowledges the feedback from the other members of the
IETF Atom Publishing working group during the development of this
specification.
Author's Address
James M Snell
Phone:
Email: jasnell@gmail.com
URI: http://snellspace.com
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