GENWiki

Internet Engineering Task Force (IETF) M. Amundsen Request for Comments: 6573 April 2012 Category: Informational ISSN: 2070-1721

               The Item and Collection Link Relations

Abstract

 RFC 5988 standardized a means of indicating the relationships between
 resources on the Web. This specification defines a pair of reciprocal
 link relation types that may be used to express the relationship
 between a collection and its members.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.

 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.

 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6573.

Copyright Notice

 Copyright (c) 2012 IETF Trust and the persons identified as the
 document authors.  All rights reserved.

 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

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1. Introduction

 RFC 5988 standardized a means of indicating the relationships between
 resources on the Web. This specification defines a pair of reciprocal
 link relation types that may be used to express the relationship
 between a collection and its members.

 These link relation types can be applied to a wide range of use cases
 across multiple media types.  For example, the 'collection' and
 'item' link relation types are used in these media types:

 1.  OpenSearch 1.1: see Section 4.5.4.1 of [OpenSearch]

 2.  Maze+XML: see [Maze]

 3.  Collection+JSON: see [CollectionJSON]

2. Link Relations

 The following link relations are defined.

2.1. 'item'

 When included in a resource that represents a collection, the 'item'
 link relation identifies a target resource that represents a member
 of that collection.

 For example, if a resource represents a catalog of products, that
 same representation may include one or more links to resources that
 represent members of that catalog.

 <html>
 ...
   <h1>Product Group X Listing</h1>
   ...
   <a href="..." rel="item">View Product X001</a>
   <a href="..." rel="item">View Product X002</a>
   ...
 </html>

 or, in the case of a Link Header field

 Link: <...>; rel="item"; title="View Product X001"
 Link: <...>; rel="item"; title="View Product X002"

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2.2. 'collection'

 When included in a resource that represents a member of a collection,
 the 'collection' link relation identifies a target resource that
 represents a collection of which the context resource is a member.

 For example, if a resource represents a single product in a catalog,
 that same representation may include a link to a resource that
 represents a product group to which this single product belongs:

 <a href="..." rel="collection">Return to Product Group X</a>

 or, in the case of a Link Header field

 Link: <...>; rel="collection"; title="Return to Product Group X"

 Since it is possible that a resource could be a member of multiple
 collections, multiple 'collection' link relations may appear within
 the same representation:

 <a href="..." rel="collection">View other widgets</a>
 <a href="..." rel="collection">View all discontinued items</a>

 The target resource representation need not be restricted to
 representing a list.  It may simply be a document that provides
 details on the collection of which the context resource is a member:

 Link: <...>; rel="collection";
       title="Shakespeare's Collected Works - A History"

 It should also be noted that the same link might represent an 'item'
 in one collection as well as a 'collection' itself.  In this case,
 both link relation values can be applied to the same link:

 Link: <...>; rel="collection item";
       title="A Review of Issac Asimov's Collected Works - Vol. I"

3. IANA Considerations

 IANA has registered the 'collection' and 'item' link relations below
 as per [RFC5988].

3.1. 'item' Link Relation Registration

 Relation Name:

    item

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 Description:

    The target IRI points to a resource that is a member of the
    collection represented by the context IRI.

 Reference:

    See Section 2

3.2. 'collection' Link Relation Registration

 Relation Name:

    collection

 Description:

    The target IRI points to a resource that represents the collection
    resource for the context IRI.

 Reference:

    See Section 2

4. Security Considerations

 The two link relation types defined in this document do not introduce
 any new security issues to those which are discussed in Section 7 of
 RFC5988 [RFC5988].

5. Internationalisation Considerations

 The 'item' and 'collection' link relation types do not have any
 internationalization considerations other than those which are
 discussed in Section 8 of RFC5988 [RFC5988].

6. References

6.1. Normative References

 [RFC5988]         Nottingham, M., "Web Linking", RFC 5988,
                   October 2010.

6.2. Informative References

 [CollectionJSON]  Amundsen, M., "Collection+JSON - Document Format",
                   Web Page , July 2011,
                   <http://www.iana.org/assignments/media-types>.

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 [Maze]            Amundsen, M., "Maze+XML - Format", Web Page ,
                   December 2010,
                   <http://www.iana.org/assignments/media-types>.

 [OpenSearch]      Clinton, D., "Open Search 1.1", Work in Progress ,
                   March 2011, <http://www.opensearch.org/
                   Specifications/OpenSearch/1.1/>.

Appendix A. Acknowledgements

 The author gratefully acknowledges the contributions of Julian
 Reschke and Mykyta Yevstifeyev.

Author's Address

 Mike Amundsen

 EMail: mca@amundsen.com
 URI:   http://amundsen.com

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