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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/