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2 Network Working Group E. Wilde
3 Internet-Draft UC Berkeley
4 Updates: 4287 (if approved) January 22, 2014
5 Intended status: Informational
6 Expires: July 26, 2014
8 Profile Support for the Atom Syndication Format
9 draft-wilde-atom-profile-03
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 July 26, 2014.
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 5. Implementation Status . . . . . . . . . . . . . . . . . . . . . 6
72 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
73 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 7
74 8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 7
75 8.1. From -02 to -03 . . . . . . . . . . . . . . . . . . . . . . 7
76 8.2. From -01 to -02 . . . . . . . . . . . . . . . . . . . . . . 7
77 8.3. From -00 to -01 . . . . . . . . . . . . . . . . . . . . . . 8
78 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
79 9.1. Normative References . . . . . . . . . . . . . . . . . . . 8
80 9.2. Informative References . . . . . . . . . . . . . . . . . . 8
81 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 9
82 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
84 1. Introduction
86 The Atom Syndication Format "is an XML-based document format that
87 describes lists of related information known as 'feeds'. Feeds are
88 composed of a number of items, known as 'entries', each with an
89 extensible set of attached metadata. For example, each entry has a
90 title." [RFC4287]
92 Profiles "can be described as additional semantics that can be used
93 to process a resource representation, such as constraints,
94 conventions, extensions, or any other aspects that do not alter the
95 basic media type semantics. A profile MUST NOT change the semantics
96 of the resource representation when processed without profile
97 knowledge, so that clients both with and without knowledge of a
98 profiled resource can safely use the same representation." [RFC6906]
100 Profiles are identified by URI, and their use can be indicated for a
101 representation by adding a link with the registered "profile" link
102 relation type, linking to the profile URI. While this is sufficient
103 to represent the fact that a certain representation is using a
104 profile, it does not make that fact visible outside of this
105 representation. Ideally, peers communicating their media type, for
106 example when communicating via Hypertext Transfer Protocol (HTTP)
107 [RFC2616], should be able to indicate the support of certain profiles
108 through the media type identifier itself, without changing the base
109 media type.
111 Because Atom supports generic links through its element,
112 "profile" links can be easily added to a feed, indicating that this
113 feed does adhere to a certain profile. However, on the media type
114 level, this feed would still be labeled as application/atom+xml,
115 making the profile invisible on that level and thus not allowing it
116 to be used in interactions such as content negotiation in HTTP.
118 This specification adds a "profile" media type parameter to the
119 application/atom+xml media type, thereby making it possible for
120 profiles to be exposed at the media type level. Apart from adding
121 that one media type parameter, this specification does not change
122 anything about the Atom format itself, or its media type
123 registration.
125 2. Examples
127 Adding a "profile" parameter to the Atom media type adds visibility
128 of profiles at the media type level, for example when alternative
129 profiles are supported by a service. It might also help to further
130 "specialize" a media type in environments where such a
131 "specialization" is useful. Two examples are intended to illustrate
132 these two scenarios.
134 2.1. Profiles for Alternatives
136 For example, when linking to feeds of media-oriented services, it
137 would be possible to expose two feeds, one using MediaRSS, and the
138 other one using Podcasts. Both formats roughly cover the same
139 functionality as media-oriented feed-based extensions, but by having
140 the ability to expose their capabilities at the media type level,
141 HTTP mechanisms and conversations can be used to distinguish between
142 these formats.
144 In some cases it may be possible to support more than one profile,
145 and then it is up for the service to decide whether these should be
146 exposed in one representation (which can be exposed by linking to
147 multiple profiles from the resource representation and/or in the
148 media type parameter), or whether there should be two
149 representations, one for each profile. This decision will probably
150 depend on implementation complexity, the trade-off between navigation
151 complexity (two representations with one profile each) and processing
152 complexity, and also the size of the profile data, because in
153 particular in the case of overlapping profiles, there might be many
154 redundancies.
156 Thus, which way to go for multiple profiles is not a question that
157 has one correct answer; it depends on the profiles, and on the
158 services that are built around them.
160 2.2. Profiles for Specializations
162 Feed-based services may provide additional features in feeds that are
163 represented using Atom's extension mechanisms. These additional
164 features might be useful only for those clients that support them,
165 and otherwise might add volume to a feed that is of no value to
166 general consumers. In such a scenario, specialized clients might
167 also request their specialized features via profile media type
168 parameters, and will then get the feed being "enriched" with the
169 additional features. If clients do not request such a profile or
170 request one that is not known to the server, the server responds with
171 a generic feed, still allowing them to treat the feed as a generic
172 feed (with no additional features being represented).
174 Whether services respond with profiles by default or only for
175 specific requests about a profile is a matter of policy, and will be
176 influenced by factors such as the added volume when adding profile
177 data, and the question whether profiles should only be exposed to
178 those that specifically ask for them. Since profiles are not allowed
179 to change the semantics of the media type itself, such a decision can
180 depend on the trade-off being a matter of expressivity, and not
181 whether it will break clients under some circumstances.
183 2.3. Profile URI for AtomPub
185 The Atom Publishing Protocol (AtomPub) [RFC5023] builds on Atom and
186 defines additional interactions with feeds, such as the ability to
187 POST an entry to a collection URI as a request to create a new entry
188 in that collection. AtomPub uses Atom's media type for representing
189 feeds and entries (and introduces its own media type for representing
190 category and service documents, but these are not relevant for this
191 discussion).
193 When requesting a collection URI from an AtomPub server, clients will
194 GET a feed document with no indication that the server supports
195 AtomPub. Clients are supposed to have knowledge about AtomPub
196 support, so that they know whether POST requests to the collection
197 URI might succeed. It is possible that clients send an OPTIONS
198 request to the collection URI to find out about the allowed methods,
199 but this requires an additional roundtrip, and since the AtomPub spec
200 does not explicitly mention OPTIONS, it may be the case that
201 implementations do not generally support this discovery mechanism.
203 To make AtomPub support of a collection explicit in a feed document,
204 the profile URI urn:ietf:rfc:5023 is suggested. When including this
205 profile URI in a feed, a server indicates AtomPub support:
206
207
208
210 When used with the profile parameter of the Atom media type, this
211 profile URI MAY be used to indicate that the resource is advertising
212 AtomPub support. It should be noted that AtomPub servers are not
213 required to use the AtomPub profile URI in any way (because it is not
214 a part of the AtomPub specification), but that supporting it may make
215 it easier for clients to discover the AtomPub capabilities of
216 available resources.
218 3. Profile Parameter Definition
220 The profile parameter for the application/atom+xml media type allows
221 one or more profile URIs to be specified. These profile URIs have
222 the identifier semantics defined in [RFC6906], and when appearing as
223 media type parameter, they have the same semantics as if they had
224 been associated with the resource URI through other means, such as
225 using one or more elements as children of
226 the element.
228 As a general rule, media type parameters must be quoted unless they
229 are tokens. For the "profile" media type parameter defined here,
230 this means that is must be quoted. It contains a non-empty list of
231 space-separated URIs (the profile URIs).
232 profile-param = "profile=" profile-value
233 profile-value = <"> profile-URI 0*( 1*SP profile-URI ) <">
234 profile-URI = URI
236 The "URI" in the above grammar refers to the "URI" as defined in
237 Section 3 of [RFC3986]
239 4. IANA Considerations
241 This specification updates an existing media type according to the
242 registry mechanism described in [RFC6838].
244 4.1. Atom Media Type application/atom+xml
246 The Internet media type for Atom (application/atom+xml) should be
247 updated by adding the following optional media type parameter:
249 4.1.1. Optional Parameters
251 profile: This parameter indicates that one or more profiles are used
252 in the feed, according to the definition of profiles in [RFC6906].
253 The parameter syntax is specified in Section 3 of RFC XXXX
255 5. Implementation Status
257 Note to RFC Editor: Please remove this section before publication.
259 This section records the status of known implementations of the
260 protocol defined by this specification at the time of posting of this
261 Internet-Draft, and is based on a proposal described in RFC 6982
262 [RFC6982]. The description of implementations in this section is
263 intended to assist the IETF in its decision processes in progressing
264 drafts to RFCs. Please note that the listing of any individual
265 implementation here does not imply endorsement by the IETF.
266 Furthermore, no effort has been spent to verify the information
267 presented here that was supplied by IETF contributors. This is not
268 intended as, and must not be construed to be, a catalog of available
269 implementations or their features. Readers are advised to note that
270 other implementations may exist.
272 According to RFC 6982, "this will allow reviewers and working groups
273 to assign due consideration to documents that have the benefit of
274 running code, which may serve as evidence of valuable experimentation
275 and feedback that have made the implemented protocols more mature.
276 It is up to the individual working groups to use this information as
277 they see fit".
279 ...
281 6. Security Considerations
283 There are no known security considerations for adding this optional
284 media type parameter to the application/atom+xml media type.
286 7. Open Issues
288 Note to RFC Editor: Please remove this section before publication.
290 o Monitor how the proposal for a "Profile URI Registry"
291 [I-D.lanthaler-profile-registry] is coming along. If it is
292 successful, then the proposed AtomPub Profile URI Section 2.3
293 should be included in the IANA Considerations Section 4.
295 8. Change Log
297 Note to RFC Editor: Please remove this section before publication.
299 8.1. From -02 to -03
301 o Updated author address.
303 8.2. From -01 to -02
305 o Added "Implementation Status" section (Section 5)."
307 o Added example and suggested URI for an AtomPub Profile
308 (Section 2.3)
310 o Changed IANA section to only request adding a "profile" media type
311 parameter (instead of providing a complete media type registration
312 template).
314 o Added "Open Issues" section (Section 7) and reminder to check the
315 progress of the "Profile URI Registry" draft.
317 o Updating "Implementation Status" section to refer to RFC 6982
318 [RFC6982].
320 o Adding "Security Considerations" section (Section 6)
322 8.3. From -00 to -01
324 o Fixed typos.
326 o Removed the requirement to percent-encode URIs in the profile
327 parameter.
329 o Added example for media type specialization.
331 9. References
333 9.1. Normative References
335 [RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
336 Types", RFC 3023, January 2001.
338 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
339 Resource Identifier (URI): Generic Syntax", STD 66,
340 RFC 3986, January 2005.
342 [RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
343 Syndication Format", RFC 4287, December 2005.
345 [RFC6906] Wilde, E., "The 'profile' Link Relation Type", RFC 6906,
346 March 2013.
348 9.2. Informative References
350 [I-D.lanthaler-profile-registry]
351 Lanthaler, M., "The IETF Profile URI Registry",
352 draft-lanthaler-profile-registry-02 (work in progress),
353 June 2013.
355 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
356 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
357 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
359 [RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing
360 Protocol", RFC 5023, October 2007.
362 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
363 Specifications and Registration Procedures", BCP 13,
364 RFC 6838, January 2013.
366 [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
367 Code: The Implementation Status Section", RFC 6982,
368 July 2013.
370 URIs
372 [1]
374 [2]
376 Appendix A. Acknowledgements
378 Thanks for comments and suggestions provided by Markus Lanthaler and
379 Peter Rushforth.
381 Author's Address
383 Erik Wilde
384 UC Berkeley
386 Email: dret@berkeley.edu
387 URI: http://dret.net/netdret/