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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'RFC3023' is defined on line 357, but no explicit reference was found in the text ** Obsolete normative reference: RFC 3023 (Obsoleted by RFC 7303) -- Obsolete informational reference (is this intentional?): RFC 2616 (Obsoleted by RFC 7230, RFC 7231, RFC 7232, RFC 7233, RFC 7234, RFC 7235) -- Obsolete informational reference (is this intentional?): RFC 6982 (Obsoleted by RFC 7942) Summary: 3 errors (**), 0 flaws (~~), 2 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 UC Berkeley 4 Updates: 4287 (if approved) July 23, 2014 5 Intended status: Informational 6 Expires: January 24, 2015 8 Profile Support for the Atom Syndication Format 9 draft-wilde-atom-profile-04 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 [1]. 28 Online access to all versions and files is available on github [2]. 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 24, 2015. 47 Copyright Notice 48 Copyright (c) 2014 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 4.2. AtomPub Profile URI . . . . . . . . . . . . . . . . . . . . 6 72 5. Implementation Status . . . . . . . . . . . . . . . . . . . . . 7 73 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 74 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 7 75 8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 7 76 8.1. From -03 to -04 . . . . . . . . . . . . . . . . . . . . . . 8 77 8.2. From -02 to -03 . . . . . . . . . . . . . . . . . . . . . . 8 78 8.3. From -01 to -02 . . . . . . . . . . . . . . . . . . . . . . 8 79 8.4. From -00 to -01 . . . . . . . . . . . . . . . . . . . . . . 8 80 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 81 9.1. Normative References . . . . . . . . . . . . . . . . . . . 8 82 9.2. Informative References . . . . . . . . . . . . . . . . . . 9 83 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 9 84 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 86 1. Introduction 88 The Atom Syndication Format "is an XML-based document format that 89 describes lists of related information known as 'feeds'. Feeds are 90 composed of a number of items, known as 'entries', each with an 91 extensible set of attached metadata. For example, each entry has a 92 title." [RFC4287] 94 Profiles "can be described as additional semantics that can be used 95 to process a resource representation, such as constraints, 96 conventions, extensions, or any other aspects that do not alter the 97 basic media type semantics. A profile MUST NOT change the semantics 98 of the resource representation when processed without profile 99 knowledge, so that clients both with and without knowledge of a 100 profiled resource can safely use the same representation." [RFC6906] 102 Profiles are identified by URI, and their use can be indicated for a 103 representation by adding a link with the registered "profile" link 104 relation type, linking to the profile URI. While this is sufficient 105 to represent the fact that a certain representation is using a 106 profile, it does not make that fact visible outside of this 107 representation. Ideally, peers communicating their media type, for 108 example when communicating via Hypertext Transfer Protocol (HTTP) 109 [RFC2616], should be able to indicate the support of certain profiles 110 through the media type identifier itself, without changing the base 111 media type. 113 Because Atom supports generic links through its element, 114 "profile" links can be easily added to a feed, indicating that this 115 feed does adhere to a certain profile. However, on the media type 116 level, this feed would still be labeled as application/atom+xml, 117 making the profile invisible on that level and thus not allowing it 118 to be used in interactions such as content negotiation in HTTP. 120 This specification adds a "profile" media type parameter to the 121 application/atom+xml media type, thereby making it possible for 122 profiles to be exposed at the media type level. Apart from adding 123 that one media type parameter, this specification does not change 124 anything about the Atom format itself, or its media type 125 registration. 127 2. Examples 129 Adding a "profile" parameter to the Atom media type adds visibility 130 of profiles at the media type level, for example when alternative 131 profiles are supported by a service. It might also help to further 132 "specialize" a media type in environments where such a 133 "specialization" is useful. Two examples are intended to illustrate 134 these two scenarios. 136 2.1. Profiles for Alternatives 138 For example, when linking to feeds of media-oriented services, it 139 would be possible to expose two feeds, one using MediaRSS, and the 140 other one using Podcasts. Both formats roughly cover the same 141 functionality as media-oriented feed-based extensions, but by having 142 the ability to expose their capabilities at the media type level, 143 HTTP mechanisms and conversations can be used to distinguish between 144 these formats. 146 In some cases it may be possible to support more than one profile, 147 and then it is up for the service to decide whether these should be 148 exposed in one representation (which can be exposed by linking to 149 multiple profiles from the resource representation and/or in the 150 media type parameter), or whether there should be two 151 representations, one for each profile. This decision will probably 152 depend on implementation complexity, the trade-off between navigation 153 complexity (two representations with one profile each) and processing 154 complexity, and also the size of the profile data, because in 155 particular in the case of overlapping profiles, there might be many 156 redundancies. 158 Thus, which way to go for multiple profiles is not a question that 159 has one correct answer; it depends on the profiles, and on the 160 services that are built around them. 162 2.2. Profiles for Specializations 164 Feed-based services may provide additional features in feeds that are 165 represented using Atom's extension mechanisms. These additional 166 features might be useful only for those clients that support them, 167 and otherwise might add volume to a feed that is of no value to 168 general consumers. In such a scenario, specialized clients might 169 also request their specialized features via profile media type 170 parameters, and will then get the feed being "enriched" with the 171 additional features. If clients do not request such a profile or 172 request one that is not known to the server, the server responds with 173 a generic feed, still allowing them to treat the feed as a generic 174 feed (with no additional features being represented). 176 Whether services respond with profiles by default or only for 177 specific requests about a profile is a matter of policy, and will be 178 influenced by factors such as the added volume when adding profile 179 data, and the question whether profiles should only be exposed to 180 those that specifically ask for them. Since profiles are not allowed 181 to change the semantics of the media type itself, such a decision can 182 depend on the trade-off being a matter of expressivity, and not 183 whether it will break clients under some circumstances. 185 2.3. Profile URI for AtomPub 187 The Atom Publishing Protocol (AtomPub) [RFC5023] builds on Atom and 188 defines additional interactions with feeds, such as the ability to 189 POST an entry to a collection URI as a request to create a new entry 190 in that collection. AtomPub uses Atom's media type for representing 191 feeds and entries (and introduces its own media type for representing 192 category and service documents, but these are not relevant for this 193 discussion). 195 When requesting a collection URI from an AtomPub server, clients will 196 GET a feed document with no indication that the server supports 197 AtomPub. Clients are supposed to have knowledge about AtomPub 198 support, so that they know whether POST requests to the collection 199 URI might succeed. It is possible that clients send an OPTIONS 200 request to the collection URI to find out about the allowed methods, 201 but this requires an additional roundtrip, and since the AtomPub spec 202 does not explicitly mention OPTIONS, it may be the case that 203 implementations do not generally support this discovery mechanism. 205 To make AtomPub support of a collection explicit in a feed document, 206 the profile URI urn:ietf:rfc:5023 is defined. When including this 207 profile URI in a feed, a server indicates AtomPub support: 208 209 210 212 When used with the profile parameter of the Atom media type, this 213 profile URI MAY be used to indicate that the resource is advertising 214 AtomPub support. It should be noted that AtomPub servers are not 215 required to use the AtomPub profile URI in any way (because it is not 216 a part of the AtomPub specification), but that supporting it may make 217 it easier for clients to discover the AtomPub capabilities of 218 available resources. 220 3. Profile Parameter Definition 222 The profile parameter for the application/atom+xml media type allows 223 one or more profile URIs to be specified. These profile URIs have 224 the identifier semantics defined in [RFC6906], and when appearing as 225 media type parameter, they have the same semantics as if they had 226 been associated with the resource URI through other means, such as 227 using one or more elements as children of 228 the element. 230 As a general rule, media type parameters must be quoted unless they 231 are tokens. For the "profile" media type parameter defined here, 232 this means that is must be quoted. It contains a non-empty list of 233 space-separated URIs (the profile URIs). 234 profile-param = "profile=" profile-value 235 profile-value = <"> profile-URI 0*( 1*SP profile-URI ) <"> 236 profile-URI = URI 238 The "URI" in the above grammar refers to the "URI" as defined in 239 Section 3 of [RFC3986] 241 4. IANA Considerations 243 This specification updates an existing media type according to the 244 registry mechanism described in [RFC6838]. 246 4.1. Atom Media Type application/atom+xml 248 The Internet media type for Atom (application/atom+xml) should be 249 updated by adding the following optional media type parameter: 251 4.1.1. Optional Parameters 253 profile: This parameter indicates that one or more profiles are used 254 in the feed, according to the definition of profiles in [RFC6906]. 255 The parameter syntax is specified in Section 3 of RFC XXXX 257 4.2. AtomPub Profile URI 259 The AtomPub Profile URI urn:ietf:rfc:5023 should be added to the 260 registry of Profile URIs established by [RFC7284]. The registration 261 should use the following information: 263 Profile URI: urn:ietf:rfc:5023 265 Common Name: Atom Publishing Protocol (AtomPub) Profile 267 Description: When using this profile URI for a resource using the 268 application/atom+xml media type, a server indicates AtomPub 269 support. 271 Reference: [RFC5023] and RFC XXXX 273 5. Implementation Status 275 Note to RFC Editor: Please remove this section before publication. 277 This section records the status of known implementations of the 278 protocol defined by this specification at the time of posting of this 279 Internet-Draft, and is based on a proposal described in RFC 6982 280 [RFC6982]. The description of implementations in this section is 281 intended to assist the IETF in its decision processes in progressing 282 drafts to RFCs. Please note that the listing of any individual 283 implementation here does not imply endorsement by the IETF. 284 Furthermore, no effort has been spent to verify the information 285 presented here that was supplied by IETF contributors. This is not 286 intended as, and must not be construed to be, a catalog of available 287 implementations or their features. Readers are advised to note that 288 other implementations may exist. 290 According to RFC 6982, "this will allow reviewers and working groups 291 to assign due consideration to documents that have the benefit of 292 running code, which may serve as evidence of valuable experimentation 293 and feedback that have made the implemented protocols more mature. 294 It is up to the individual working groups to use this information as 295 they see fit". 297 ... 299 6. Security Considerations 301 There are no known security considerations for adding this optional 302 media type parameter to the application/atom+xml media type. 304 7. Open Issues 306 Note to RFC Editor: Please remove this section before publication. 308 o Are there other Atom profile URIs that could be registered as a 309 part of this draft? 311 8. Change Log 313 Note to RFC Editor: Please remove this section before publication. 315 8.1. From -03 to -04 317 o Moved "The Profile URI Registry" from I-D to RFC. 319 o Adding AtomPub Profile registration according to [RFC7284]. 321 8.2. From -02 to -03 323 o Updated author address. 325 8.3. From -01 to -02 327 o Added "Implementation Status" section (Section 5)." 329 o Added example and suggested URI for an AtomPub Profile 330 (Section 2.3) 332 o Changed IANA section to only request adding a "profile" media type 333 parameter (instead of providing a complete media type registration 334 template). 336 o Added "Open Issues" section (Section 7) and reminder to check the 337 progress of the "Profile URI Registry" draft. 339 o Updating "Implementation Status" section to refer to RFC 6982 340 [RFC6982]. 342 o Adding "Security Considerations" section (Section 6) 344 8.4. From -00 to -01 346 o Fixed typos. 348 o Removed the requirement to percent-encode URIs in the profile 349 parameter. 351 o Added example for media type specialization. 353 9. References 355 9.1. Normative References 357 [RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media 358 Types", RFC 3023, January 2001. 360 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 361 Resource Identifier (URI): Generic Syntax", STD 66, 362 RFC 3986, January 2005. 364 [RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom 365 Syndication Format", RFC 4287, December 2005. 367 [RFC6906] Wilde, E., "The 'profile' Link Relation Type", RFC 6906, 368 March 2013. 370 [RFC7284] Lanthaler, M., "The Profile URI Registry", RFC 7284, 371 June 2014. 373 9.2. Informative References 375 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 376 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 377 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 379 [RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing 380 Protocol", RFC 5023, October 2007. 382 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 383 Specifications and Registration Procedures", BCP 13, 384 RFC 6838, January 2013. 386 [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 387 Code: The Implementation Status Section", RFC 6982, 388 July 2013. 390 URIs 392 [1] 394 [2] 396 Appendix A. Acknowledgements 398 Thanks for comments and suggestions provided by Markus Lanthaler and 399 Peter Rushforth. 401 Author's Address 403 Erik Wilde 404 UC Berkeley 406 Email: dret@berkeley.edu 407 URI: http://dret.net/netdret/