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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: '4' is defined on line 339, but no explicit reference was found in the text ** 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) -- Obsolete informational reference (is this intentional?): RFC 6982 (ref. '8') (Obsoleted by RFC 7942) == Outdated reference: A later version (-05) exists of draft-lanthaler-profile-registry-02 Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 4 comments (--).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) July 29, 2013 5 Intended status: Informational 6 Expires: January 30, 2014 8 Profile Support for the Atom Syndication Format 9 draft-wilde-atom-profile-02 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 adds an optional "profile" 17 media type parameter to the Atom media type. This allows profiles to 18 become visible at the media type level, so that servers as well as 19 clients can indicate support for specific Atom profiles in 20 conversations, for example when communicating via HTTP. This 21 specification updates RFC 4287 by adding the "profile" media type 22 parameter to the application/atom+xml media type registration. 24 Note to Readers 26 This draft should be discussed on the atom-syntax mailing list [10]. 28 Online access to all versions and files is available on github [11]. 30 Status of this Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on January 30, 2014. 47 Copyright Notice 48 Copyright (c) 2013 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 65 2.1. Profiles for Alternatives . . . . . . . . . . . . . . . . . 4 66 2.2. Profiles for Specializations . . . . . . . . . . . . . . . 4 67 2.3. Profile URI for AtomPub . . . . . . . . . . . . . . . . . . 5 68 3. Profile Parameter Definition . . . . . . . . . . . . . . . . . 5 69 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 70 4.1. Atom Media Type application/atom+xml . . . . . . . . . . . 6 71 5. Implementation Status . . . . . . . . . . . . . . . . . . . . . 6 72 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 73 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 7 74 8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 7 75 8.1. From -01 to -02 . . . . . . . . . . . . . . . . . . . . . . 7 76 8.2. From -00 to -01 . . . . . . . . . . . . . . . . . . . . . . 8 77 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 78 9.1. Normative References . . . . . . . . . . . . . . . . . . . 8 79 9.2. Non-Normative References . . . . . . . . . . . . . . . . . 8 80 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 9 81 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 83 1. Introduction 85 The Atom Syndication Format "is an XML-based document format that 86 describes lists of related information known as 'feeds'. Feeds are 87 composed of a number of items, known as 'entries', each with an 88 extensible set of attached metadata. For example, each entry has a 89 title." [1] 91 Profiles "can be described as additional semantics that can be used 92 to process a resource representation, such as constraints, 93 conventions, extensions, or any other aspects that do not alter the 94 basic media type semantics. A profile MUST NOT change the semantics 95 of the resource representation when processed without profile 96 knowledge, so that clients both with and without knowledge of a 97 profiled resource can safely use the same representation." [2] 99 Profiles are identified by URI, and their use can be indicated for a 100 representation by adding a link with the registered "profile" link 101 relation type, linking to the profile URI. While this is sufficient 102 to represent the fact that a certain representation is using a 103 profile, it does not make that fact visible outside of this 104 representation. Ideally, peers communicating their media type, for 105 example when communicating via Hypertext Transfer Protocol (HTTP) 106 [5], should be able to indicate the support of certain profiles 107 through the media type identifier itself, without changing the base 108 media type. 110 Because Atom supports generic links through its element, 111 "profile" links can be easily added to a feed, indicating that this 112 feed does adhere to a certain profile. However, on the media type 113 level, this feed would still be labeled as application/atom+xml, 114 making the profile invisible on that level and thus not allowing it 115 to be used in interactions such as content negotiation in HTTP. 117 This specification adds a "profile" media type parameter to the 118 application/atom+xml media type, thereby making it possible for 119 profiles to be exposed at the media type level. Apart from adding 120 that one media type parameter, this specification does not change 121 anything about the Atom format itself, or its media type 122 registration. 124 2. Examples 126 Adding a "profile" parameter to the Atom media type adds visibility 127 of profiles at the media type level, for example when alternative 128 profiles are supported by a service. It might also help to further 129 "specialize" a media type in environments where such a 130 "specialization" is useful. Two examples are intended to illustrate 131 these two scenarios. 133 2.1. Profiles for Alternatives 135 For example, when linking to feeds of media-oriented services, it 136 would be possible to expose two feeds, one using MediaRSS, and the 137 other one using Podcasts. Both formats roughly cover the same 138 functionality as media-oriented feed-based extensions, but by having 139 the ability to expose their capabilities at the media type level, 140 HTTP mechanisms and conversations can be used to distinguish between 141 these formats. 143 In some cases it may be possible to support more than one profile, 144 and then it is up for the service to decide whether these should be 145 exposed in one representation (which can be exposed by linking to 146 multiple profiles from the resource representation and/or in the 147 media type parameter), or whether there should be two 148 representations, one for each profile. This decision will probably 149 depend on implementation complexity, the trade-off between navigation 150 complexity (two representations with one profile each) and processing 151 complexity, and also the size of the profile data, because in 152 particular in the case of overlapping profiles, there might be many 153 redundancies. 155 Thus, which way to go for multiple profiles is not a question that 156 has one correct answer; it depends on the profiles, and on the 157 services that are built around them. 159 2.2. Profiles for Specializations 161 Feed-based services may provide additional features in feeds that are 162 represented using Atom's extension mechanisms. These additional 163 features might be useful only for those clients that support them, 164 and otherwise might add volume to a feed that is of no value to 165 general consumers. In such a scenario, specialized clients might 166 also request their specialized features via profile media type 167 parameters, and will then get the feed being "enriched" with the 168 additional features. If clients do not request such a profile or 169 request one that is not known to the server, the server responds with 170 a generic feed, still allowing them to treat the feed as a generic 171 feed (with no additional features being represented). 173 Whether services respond with profiles by default or only for 174 specific requests about a profile is a matter of policy, and will be 175 influenced by factors such as the added volume when adding profile 176 data, and the question whether profiles should only be exposed to 177 those that specifically ask for them. Since profiles are not allowed 178 to change the semantics of the media type itself, such a decision can 179 depend on the trade-off being a matter of expressivity, and not 180 whether it will break clients under some circumstances. 182 2.3. Profile URI for AtomPub 184 The Atom Publishing Protocol (AtomPub) [6] builds on Atom and defines 185 additional interactions with feeds, such as the ability to POST an 186 entry to a collection URI as a request to create a new entry in that 187 collection. AtomPub uses Atom's media type for representing feeds 188 and entries (and introduces its own media type for representing 189 category and service documents, but these are not relevant for this 190 discussion). 192 When requesting a collection URI from an AtomPub server, clients will 193 GET a feed document with no indication that the server supports 194 AtomPub. Clients are supposed to have knowledge about AtomPub 195 support, so that they know whether POST requests to the collection 196 URI might succeed. It is possible that clients send an OPTIONS 197 request to the collection URI to find out about the allowed methods, 198 but this requires an additional roundtrip, and since the AtomPub spec 199 does not explicitly mention OPTIONS, it may be the case that 200 implementations do not generally support this discovery mechanism. 202 To make AtomPub support of a collection explicit in a feed document, 203 the profile URI urn:ietf:rfc:5023 is suggested. When including this 204 profile URI in a feed, a server indicates AtomPub support: 205 206 207 209 When used with the profile parameter of the Atom media type, this 210 profile URI MAY be used to indicate that the resource is advertising 211 AtomPub support. It should be noted that AtomPub servers are not 212 required to use the AtomPub profile URI in any way (because it is not 213 a part of the AtomPub specification), but that supporting it may make 214 it easier for clients to discover the AtomPub capabilities of 215 available resources. 217 3. Profile Parameter Definition 219 The profile parameter for the application/atom+xml media type allows 220 one or more profile URIs to be specified. These profile URIs have 221 the identifier semantics defined in [2], and when appearing as media 222 type parameter, they have the same semantics as if they had been 223 associated with the resource URI through other means, such as using 224 one or more elements as children of the 225 element. 227 As a general rule, media type parameters must be quoted unless they 228 are tokens. For the "profile" media type parameter defined here, 229 this means that is must be quoted. It contains a non-empty list of 230 space-separated URIs (the profile URIs). 231 profile-param = "profile=" profile-value 232 profile-value = <"> profile-URI 0*( 1*SP profile-URI ) <"> 233 profile-URI = URI 235 The "URI" in the above grammar refers to the "URI" as defined in 236 Section 3 of [3] 238 4. IANA Considerations 240 This specification updates an existing media type according to the 241 registry mechanism described in [7]. 243 4.1. Atom Media Type application/atom+xml 245 The Internet media type for Atom (application/atom+xml) should be 246 updated by adding the following optional media type parameter: 248 4.1.1. Optional Parameters 250 profile: This parameter indicates that one or more profiles are used 251 in the feed, according to the definition of profiles in [2]. The 252 parameter syntax is specified in Section 3 of RFC XXXX 254 5. Implementation Status 256 Note to RFC Editor: Please remove this section before publication. 258 This section records the status of known implementations of the 259 protocol defined by this specification at the time of posting of this 260 Internet-Draft, and is based on a proposal described in RFC 6982 [8]. 261 The description of implementations in this section is intended to 262 assist the IETF in its decision processes in progressing drafts to 263 RFCs. Please note that the listing of any individual implementation 264 here does not imply endorsement by the IETF. Furthermore, no effort 265 has been spent to verify the information presented here that was 266 supplied by IETF contributors. This is not intended as, and must not 267 be construed to be, a catalog of available implementations or their 268 features. Readers are advised to note that other implementations may 269 exist. 271 According to RFC 6982, "this will allow reviewers and working groups 272 to assign due consideration to documents that have the benefit of 273 running code, which may serve as evidence of valuable experimentation 274 and feedback that have made the implemented protocols more mature. 275 It is up to the individual working groups to use this information as 276 they see fit". 278 ... 280 6. Security Considerations 282 There are no known security considerations for adding this optional 283 media type parameter to the application/atom+xml media type. 285 7. Open Issues 287 Note to RFC Editor: Please remove this section before publication. 289 o Monitor how the proposal for a "Profile URI Registry" [9] is 290 coming along. If it is successful, then the proposed AtomPub 291 Profile URI Section 2.3 should be included in the IANA 292 Considerations Section 4. 294 8. Change Log 296 Note to RFC Editor: Please remove this section before publication. 298 8.1. From -01 to -02 300 o Added "Implementation Status" section (Section 5)." 302 o Added example and suggested URI for an AtomPub Profile 303 (Section 2.3) 305 o Changed IANA section to only request adding a "profile" media type 306 parameter (instead of providing a complete media type registration 307 template). 309 o Added "Open Issues" section (Section 7) and reminder to check the 310 progress of the "Profile URI Registry" draft. 312 o Updating "Implementation Status" section to refer to RFC 6982 [8]. 314 o Adding "Security Considerations" section (Section 6) 316 8.2. From -00 to -01 318 o Fixed typos. 320 o Removed the requirement to percent-encode URIs in the profile 321 parameter. 323 o Added example for media type specialization. 325 9. References 327 9.1. Normative References 329 [1] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom Syndication 330 Format", RFC 4287, December 2005. 332 [2] Wilde, E., "The 'profile' Link Relation Type", RFC 6906, 333 March 2013. 335 [3] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 336 Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, 337 January 2005. 339 [4] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", 340 RFC 3023, January 2001. 342 9.2. Non-Normative References 344 [5] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., 345 Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- 346 HTTP/1.1", RFC 2616, June 1999. 348 [6] Gregorio, J. and B. de hOra, "The Atom Publishing Protocol", 349 RFC 5023, October 2007. 351 [7] Freed, N., Klensin, J., and T. Hansen, "Media Type 352 Specifications and Registration Procedures", BCP 13, RFC 6838, 353 January 2013. 355 [8] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: 356 The Implementation Status Section", RFC 6982, July 2013. 358 [9] Lanthaler, M., "The IETF Profile URI Registry", 359 draft-lanthaler-profile-registry-02 (work in progress), 360 June 2013. 362 URIs 364 [10] 366 [11] 368 Appendix A. Acknowledgements 370 Thanks for comments and suggestions provided by Markus Lanthaler and 371 Peter Rushforth. 373 Author's Address 375 Erik Wilde 376 EMC 377 6801 Koll Center Parkway 378 Pleasanton, CA 94566 379 U.S.A. 381 Phone: +1-925-6006244 382 Email: erik.wilde@emc.com 383 URI: http://dret.net/netdret/