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Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Informational RFC: RFC 6906 (ref. '2') ** Obsolete normative reference: RFC 3023 (ref. '4') (Obsoleted by RFC 7303) -- Obsolete informational reference (is this intentional?): RFC 2616 (ref. '5') (Obsoleted by RFC 7230, RFC 7231, RFC 7232, RFC 7233, RFC 7234, RFC 7235) Summary: 4 errors (**), 0 flaws (~~), 1 warning (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group E. Wilde 3 Internet-Draft EMC 4 Updates: 4287 (if approved) April 26, 2013 5 Intended status: Standards Track 6 Expires: October 28, 2013 8 Profile Support for the Atom Syndication Format 9 draft-wilde-atom-profile-01 11 Abstract 13 The Atom syndication format is a generic XML format for representing 14 collections. Profiles are one way how Atom feeds can indicate that 15 they support specific extensions. To make this support visible on 16 the media type level, this specification re-registers the Atom media 17 type, and adds a "profile" media type parameter. This allows 18 profiles to become visible at the media type level, so that servers 19 as well as clients can indicate support for specific Atom profiles in 20 conversations, for example when communicating via HTTP. 22 Note to Readers 24 This draft should be discussed on the atom-syntax mailing list [7]. 26 Online access to all versions and files is available on github [8]. 28 Status of this Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at http://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on October 28, 2013. 45 Copyright Notice 47 Copyright (c) 2013 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2.1. Profiles for Alternatives . . . . . . . . . . . . . . . . . 4 65 2.2. Profiles for Specializations . . . . . . . . . . . . . . . 4 66 3. Profile Parameter Definition . . . . . . . . . . . . . . . . . 5 67 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 68 4.1. Atom Media Type application/atom+xml . . . . . . . . . . . 5 69 5. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 7 70 5.1. From -00 to -01 . . . . . . . . . . . . . . . . . . . . . . 7 71 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 72 6.1. Normative References . . . . . . . . . . . . . . . . . . . 7 73 6.2. Non-Normative References . . . . . . . . . . . . . . . . . 8 74 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 8 75 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 77 1. Introduction 79 The Atom Syndication Format "is an XML-based document format that 80 describes lists of related information known as 'feeds'. Feeds are 81 composed of a number of items, known as 'entries', each with an 82 extensible set of attached metadata. For example, each entry has a 83 title." [1] 85 Profiles "can be described as additional semantics that can be used 86 to process a resource representation, such as constraints, 87 conventions, extensions, or any other aspects that do not alter the 88 basic media type semantics. A profile MUST NOT change the semantics 89 of the resource representation when processed without profile 90 knowledge, so that clients both with and without knowledge of a 91 profiled resource can safely use the same representation." [2] 93 Profiles are identified by URI, and their use can be indicated for a 94 representation by adding a link with the registered "profile" link 95 relation type, linking to the profile URI. While this is sufficient 96 to represent the fact that a certain representation is using a 97 profile, it does not make that fact visible outside of this 98 representation. Ideally, peers communicating their media type, for 99 example when communicating via Hypertext Transfer Protocol (HTTP) 100 [5], should be able to indicate the support of certain profiles 101 through the media type identifier itself, without changing the base 102 media type. 104 Because Atom supports generic links through its element, 105 "profile" links can be easily added to a feed, indicating that this 106 feed does adhere to a certain profile. However, on the media type 107 level, this feed would still be labeled as application/atom+xml, 108 making the profile invisible on that level and thus not allowing it 109 to be used in interactions such as content negotiation in HTTP. 111 This specification adds a "profile" media type parameter to the 112 application/atom+xml media type, thereby making it possible for 113 profiles to be exposed at the media type level. Apart from adding 114 that one media type parameter, this specification does not change 115 anything about the Atom format itself, or its media type 116 registration. 118 2. Examples 120 Adding a "profile" parameter to the Atom media type adds visibility 121 of profiles at the media type level, for example when alternative 122 profiles are supported by a service. It might also help to further 123 "specialize" a media type in environments where such a 124 "specialization" is useful. Two examples are intended to illustrate 125 these two scenarios. 127 2.1. Profiles for Alternatives 129 For example, when linking to feeds of media-oriented services, it 130 would be possible to expose two feeds, one using MediaRSS, and the 131 other one using Podcasts. Both formats roughly cover the same 132 functionality as media-oriented feed-based extensions, but by having 133 the ability to expose their capabilities at the media type level, 134 HTTP mechanisms and conversations can be used to distinguish between 135 these formats. 137 In some cases it may be possible to support more than one profile, 138 and then it is up for the service to decide whether these should be 139 exposed in one representation (which can be exposed by linking to 140 multiple profiles from the resource representation and/or in the 141 media type parameter), or whether there should be two 142 representations, one for each profile. This decision will probably 143 depend on implementation complexity, the trade-off between navigation 144 complexity (two representations with one profile each) and processing 145 complexity, and also the size of the profile data, because in 146 particular in the case of overlapping profiles, there might be many 147 redundancies. 149 Thus, which way to go for multiple profiles is not a question that 150 has one correct answer; it depends on the profiles, and on the 151 services that are built around them. 153 2.2. Profiles for Specializations 155 Feed-based services may provide additional features in feeds that are 156 represented using Atom's extension mechanisms. These additional 157 features might be useful only for those clients that support them, 158 and otherwise might add volume to a feed that is of no value to 159 general consumers. In such a scenario, specialized clients might 160 also request their specialized features via profile media type 161 parameters, and will then get the feed being "enriched" with the 162 additional features. If clients do not request such a profile or 163 request one that is not known to the server, the server responds with 164 a generic feed, still allowing them to treat the feed as a generic 165 feed (with no additional features being represented). 167 Whether services respond with profiles by default or only for 168 specific requests about a profile is a matter of policy, and will be 169 influenced by factors such as the added volume when adding profile 170 data, and the question whether profiles should only be exposed to 171 those that specifically ask for them. Since profiles are not allowed 172 to change the semantics of the media type itself, such a decision can 173 depend on the trade-off being a matter of expressivity, and not 174 whether it will break clients under some circumstances. 176 3. Profile Parameter Definition 178 The profile parameter for the application/atom+xml media type allows 179 one or more profile URIs to be specified. These profile URIs have 180 the identifier semantics defined in [2], and when appearing as media 181 type parameter, they have the same semantics as if they had been 182 associated with the resource URI through other means, such as using 183 one or more elements as children of the 184 element. 186 As a general rule, media type parameters must be quoted unless they 187 are tokens. For the "profile" media type parameter defined here, 188 this means that is must be quoted. It contains a non-empty list of 189 space-separated URIs (the profile URIs). 190 profile-param = "profile=" profile-value 191 profile-value = <"> profile-URI 0*( 1*SP profile-URI ) <"> 192 profile-URI = URI 194 The "URI" in the above grammar refers to the "URI" as defined in 195 Section 3 of [3] 197 4. IANA Considerations 199 The media type registration for the media type application/atom+xml 200 should be updated according to the following registration. 202 4.1. Atom Media Type application/atom+xml 204 The Internet media type [6] for an Atom document is application/ 205 atom+xml. 207 4.1.1. Media Type Name 209 application 211 4.1.2. Subtype Name 213 atom+xml 215 4.1.3. Required Parameters 217 none 219 4.1.4. Optional Parameters 221 charset: This parameter has semantics identical to the charset 222 parameter of the "application/xml" media type as specified in [4]. 224 profile: This parameter indicates that one or more profiles are used 225 in the feed, according to the definition of profiles in [2]. The 226 parameter syntax is specified in Section 3 of RFC XXXX 228 4.1.5. Encoding Considerations 230 Identical to those of "application/xml" as described in [4], Section 231 3.2. 233 4.1.6. Security Considerations 235 As defined in [1]. In addition, as this media type uses the "+xml" 236 convention, it shares the same security considerations as described 237 in [4], Section 10. 239 4.1.7. Interoperability Considerations 241 There are no known interoperability issues. 243 4.1.8. Published Specification 245 [1], RFC XXXX 247 4.1.9. Applications which use this media type 249 Many. Atom has become a common foundation for many syndication- 250 oriented scenarios, and also has become a commonly used 251 representation for collection contents. 253 4.1.10. Magic number(s) 255 As specified for "application/xml" in [4], Section 3.2. 257 4.1.11. File extension(s) 259 .atom 261 4.1.12. Fragment Identifiers 263 As specified for "application/xml" in [4], Section 5. 265 4.1.13. Base URI 267 As specified in [4], Section 6. 269 4.1.14. Macintosh File Type Code(s) 271 TEXT 273 4.1.15. Person & email address to contact for further information 275 Mark Nottingham and Erik Wilde 277 4.1.16. Intended Usage 279 Common 281 4.1.17. Author/Change Controller 283 IESG 285 5. Change Log 287 Note to RFC Editor: Please remove this section before publication. 289 5.1. From -00 to -01 291 o Fixed typos. 293 o Removed the requirement to percent-encode URIs in the profile 294 parameter. 296 o Added example for media type specialization. 298 6. References 300 6.1. Normative References 302 [1] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom Syndication 303 Format", RFC 4287, December 2005. 305 [2] Wilde, E., "The 'profile' Link Relation Type", RFC 6906, 306 March 2013. 308 [3] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 309 Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, 310 January 2005. 312 [4] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", 313 RFC 3023, January 2001. 315 6.2. Non-Normative References 317 [5] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., 318 Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- 319 HTTP/1.1", RFC 2616, June 1999. 321 [6] Freed, N., Klensin, J., and T. Hansen, "Media Type 322 Specifications and Registration Procedures", BCP 13, RFC 6838, 323 January 2013. 325 URIs 327 [7] 329 [8] 331 Appendix A. Acknowledgements 333 Thanks for comments and suggestions provided by Markus Lanthaler. 335 Author's Address 337 Erik Wilde 338 EMC 339 6801 Koll Center Parkway 340 Pleasanton, CA 94566 341 U.S.A. 343 Phone: +1-925-6006244 344 Email: erik.wilde@emc.com 345 URI: http://dret.net/netdret/