Network Working Group E. Wilde Internet-Draft EMC Updates: 4287 (if approved) March 30, 2013 Intended status: Standards Track Expires: October 1, 2013 Profile Support for the Atom Syndication Format draft-wilde-atom-profile-00 Abstract The Atom syndication format is a generic XML format for representing collections. Profiles are one way how Atom feeds can indicate that they support specific extensions. To make this support visible on the media type level, this specification re-registers the Atom media type, and adds a "profile" media type parameter. This allows profiles to become visible at the media type level, so that servers as well as clients can indicate support for specific Atom profiles in conversations, for example when communicating via HTTP. Note to Readers This draft should be discussed on the atom-syntax mailing list [6]. Online access to all versions and files is available on github [7]. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on October 1, 2013. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. Wilde Expires October 1, 2013 [Page 1] Internet-Draft Atom Profiles March 2013 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Profile Parameter Definition . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Atom Media Type application/atom+xml . . . . . . . . . . . 5 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.1. Normative References . . . . . . . . . . . . . . . . . . . 7 5.2. Non-Normative References . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Wilde Expires October 1, 2013 [Page 2] Internet-Draft Atom Profiles March 2013 1. Introduction 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." [1] 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." [2] 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 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). [4]. 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. 2. Examples 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 Wilde Expires October 1, 2013 [Page 3] Internet-Draft Atom Profiles March 2013 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. 3. Profile Parameter Definition 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 [2], 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 element as a child of the 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 links) will not be URI-encoded, and thus properly encoding and decoding URIs in these two location is essential to implement correct processing. Wilde Expires October 1, 2013 [Page 4] Internet-Draft Atom Profiles March 2013 4. IANA Considerations The Internet media type [5] for an Atom document is application/ atom+xml. 4.1. Atom Media Type application/atom+xml This specification requests the registration of an XML-based media type for the eXtensible Access Control Markup Language (XACML). 4.1.1. Media Type Name application 4.1.2. Subtype Name atom+xml 4.1.3. Required Parameters none 4.1.4. Optional Parameters charset: This parameter has semantics identical to the charset parameter of the "application/xml" media type as specified in [3]. profile: This parameter indicates that one or more profiles are used in the feed, according to the definition of profiles in [2]. The parameter syntax is specified in of RFC XXXX (Section 3) 4.1.5. Encoding Considerations Identical to those of "application/xml" as described in [3], Section 3.2. 4.1.6. Security Considerations As defined in [1]. In addition, as this media type uses the "+xml" convention, it shares the same security considerations as described in [3], Section 10. 4.1.7. Interoperability Considerations There are no known interoperability issues. Wilde Expires October 1, 2013 [Page 5] Internet-Draft Atom Profiles March 2013 4.1.8. Published Specification [1] 4.1.9. Applications which use this media type Many. Atom has become a common foundation for many syndication- oriented scenarios, and also has become a commonly used representation for collection contents. 4.1.10. Magic number(s) As specified for "application/xml" in [3], Section 3.2. 4.1.11. File extension(s) .atom 4.1.12. Fragment Identifiers As specified for "application/xml" in [3], Section 5. 4.1.13. Base URI As specified in [3], Section 6. 4.1.14. Macintosh File Type Code(s) TEXT 4.1.15. Person & email address to contact for further information Mark Nottingham and Erik Wilde 4.1.16. Intended Usage Common 4.1.17. Author/Change Controller IESG 5. References Wilde Expires October 1, 2013 [Page 6] Internet-Draft Atom Profiles March 2013 5.1. Normative References [1] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom Syndication Format", RFC 4287, December 2005. [2] Wilde, E., "The 'profile' Link Relation Type", RFC 6906, March 2013. [3] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", RFC 3023, January 2001. 5.2. Non-Normative References [4] 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. [5] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, January 2013. URIs [6] [7] Author's Address Erik Wilde EMC 6801 Koll Center Parkway Pleasanton, CA 94566 U.S.A. Phone: +1-925-6006244 Email: erik.wilde@emc.com URI: http://dret.net/netdret/ Wilde Expires October 1, 2013 [Page 7]