Profile Support for the Atom Syndication Format

The Atom Syndication Format "is an XML-based document format that describes lists of related information known as 'feeds'. Feeds are composed of a number of items, known as 'entries', each with an extensible set of attached metadata. For example, each entry has a title." Profiles "can be described as additional semantics that can be used to process a resource representation, such as constraints, conventions, extensions, or any other aspects that do not alter the basic media type semantics. A profile MUST NOT change the semantics of the resource representation when processed without profile knowledge, so that clients both with and without knowledge of a profiled resource can safely use the same representation." Profiles are identified by URI, and can be added to a representation by adding a link with the registered "profile" link relation type, linking to the profile URI. While this is sufficient to represent the fact that a certain representation is using a profile, it does not make that fact visible outside of this representation. Ideally, peers communicating their media type should be able to indicate the support of certain profiles through the media type itself, without changing the base media type. Because Atom supports generic links through its <link/> element, "profile" links can be easily added to a feed, indicating that this feed does adhere to a certain profile. However, on the media type level, this feed would still be labeled as application/atom+xml, making the profile invisible on that level and thus not allowing it to be used in interactions such as content negotiation in the Hypertext Transfer Protocol (HTTP). . This specification adds a "profile" parameter to the application/atom+xml media type, thereby making it possible for profiles to be exposed at the media type level. Apart from adding that one media type parameter, this specification does not change anything about the Atom format itself.

Adding a "profile" parameter to the Atom media type adds visibility of profiles at the media type level. For example, when linking to feeds of media-oriented services, it would be possible to expose two feeds, one using MediaRSS, and the other using Podcasts. Both formats roughly cover the same functionality as media-oriented feed-based extensions, but by having the ability to expose their capabilities at the media type level, HTTP mechanisms and conversations can be used to distinguish between these formats. In some cases it may be possible to support more than one profile, and then it is up for the service to decide whether these should be exposed in one representation (which can be exposed by linking to multiple profiles from the resource representation and/or in the media type parameter), or whether there should be two representations, one for each profile. This decision will probably depend on implementation complexity, the trade-off between navigation complexity (two representations with one profile each) and processing complexity, and also the size of the profile data, because in particular in the case of overlapping profiles, there might be many redundacies. Thus, which way to go for multiple profiles is not a question that as one correct answer; it depends on the profiles, and on the services that are built around them.

The profile parameter for the application/atom+xml media type allows one or more profile URIs to be specified. These profile URIs have the identifier semantics defined in , and when appearing as media type parameter, they have the same semantics as if they had been associated with the resource URI through other means, such as using one or more <link profile="" href=""/> element as a child of the <feed> element. Media type parameters must be quoted unless they are tokens. For the "profile" media type parameter defined here, this means that is must be quoted, and contains a non-empty list of space-separated URI-encoded URIs.

profile-param = "profile=" profile-value profile-value = <"> profile-URI 0*( 1*SP profile-URI ) <"> profile-URI = percent-encoded-URI When processing "mprofile" media type parameters, it is therefore important to apply URI-decoding before processing the URI (such as comparing it to known profiles). This is particularly important since profile URIs in Atom content (in <link profile="" href=""/> links) will not be URI-encoded, and thus properly encoding and decoding URIs in these two location is essential to implement correct processing.

The Internet media type for an Atom document is application/atom+xml.

This specification requests the registration of an XML-based media type for the eXtensible Access Control Markup Language (XACML).

application

atom+xml

none

charset: This parameter has semantics identical to the charset parameter of the "application/xml" media type as specified in . profile: This parameter indicates that one or more profiles are used in the feed, according to the definition of profiles in . The parameter syntax is specified in of RFC XXXX

Identical to those of "application/xml" as described in , Section 3.2.

As defined in . In addition, as this media type uses the "+xml" convention, it shares the same security considerations as described in , Section 10.

There are no known interoperability issues.

Many. Atom has become a common foundation for many syndication-oriented scenarios, and also has become a commonly used representation for collection contents.

As specified for "application/xml" in , Section 3.2.

.atom

As specified for "application/xml" in , Section 5.

As specified in , Section 6.

TEXT

Mark Nottingham <mnot@mnot.net> and Erik Wilde <erik.wilde@emc.com>

Common

IESG