6573
INFORMATIONAL
The Item and Collection Link Relations
Authors: M. Amundsen
Date: April 2012
Working Group: NON WORKING GROUP
Stream: IETF
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. This document is not an Internet Standards Track specification; it is published for informational purposes.
RFC 6573
INFORMATIONAL
Internet Engineering Task Force (IETF) M. Amundsen
Request for Comments: 6573 April 2012
Category: Informational
ISSN: 2070-1721
<span class="h1">The Item and Collection Link Relations</span>
Abstract
<a href="./rfc5988">RFC 5988</a> 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 <a href="./rfc5741#section-2">Section 2 of RFC 5741</a>.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
<a href="https://www.rfc-editor.org/info/rfc6573">http://www.rfc-editor.org/info/rfc6573</a>.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
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described in the Simplified BSD License.
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<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
<a href="./rfc5988">RFC 5988</a> 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 [<a href="#ref-OpenSearch" title=""Open Search 1.1"">OpenSearch</a>]
2. Maze+XML: see [<a href="#ref-Maze" title=""Maze+XML - Format"">Maze</a>]
3. Collection+JSON: see [<a href="#ref-CollectionJSON" title=""Collection+JSON - Document Format"">CollectionJSON</a>]
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Link Relations</span>
The following link relations are defined.
<span class="h3"><a class="selflink" id="section-2.1" href="#section-2.1">2.1</a>. 'item'</span>
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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<span class="h3"><a class="selflink" id="section-2.2" href="#section-2.2">2.2</a>. 'collection'</span>
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"
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. IANA Considerations</span>
IANA has registered the 'collection' and 'item' link relations below
as per [<a href="./rfc5988" title=""Web Linking"">RFC5988</a>].
<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>. 'item' Link Relation Registration</span>
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 <a href="#section-2">Section 2</a>
<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>. 'collection' Link Relation Registration</span>
Relation Name:
collection
Description:
The target IRI points to a resource that represents the collection
resource for the context IRI.
Reference:
See <a href="#section-2">Section 2</a>
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Security Considerations</span>
The two link relation types defined in this document do not introduce
any new security issues to those which are discussed in <a href="./rfc5988#section-7">Section 7 of
RFC5988</a> [<a href="./rfc5988" title=""Web Linking"">RFC5988</a>].
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. Internationalisation Considerations</span>
The 'item' and 'collection' link relation types do not have any
internationalization considerations other than those which are
discussed in <a href="./rfc5988#section-8">Section 8 of RFC5988</a> [<a href="./rfc5988" title=""Web Linking"">RFC5988</a>].
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. References</span>
<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>. Normative References</span>
[<a id="ref-RFC5988">RFC5988</a>] Nottingham, M., "Web Linking", <a href="./rfc5988">RFC 5988</a>,
October 2010.
<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>. Informative References</span>
[<a id="ref-CollectionJSON">CollectionJSON</a>] Amundsen, M., "Collection+JSON - Document Format",
Web Page , July 2011,
<<a href="http://www.iana.org/assignments/media-types">http://www.iana.org/assignments/media-types</a>>.
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[<a id="ref-Maze">Maze</a>] Amundsen, M., "Maze+XML - Format", Web Page ,
December 2010,
<<a href="http://www.iana.org/assignments/media-types">http://www.iana.org/assignments/media-types</a>>.
[<a id="ref-OpenSearch">OpenSearch</a>] Clinton, D., <a style="text-decoration: none" href='https://www.google.com/search?sitesearch=datatracker.ietf.org%2Fdoc%2Fhtml%2F&q=inurl:draft-+%22Open+Search+1.1%22'>"Open Search 1.1"</a>, Work in Progress ,
March 2011, <<a href="http://www.opensearch.org/Specifications/OpenSearch/1.1/">http://www.opensearch.org/</a>
<a href="http://www.opensearch.org/Specifications/OpenSearch/1.1/">Specifications/OpenSearch/1.1/</a>>.
<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>. Acknowledgements</span>
The author gratefully acknowledges the contributions of Julian
Reschke and Mykyta Yevstifeyev.
Author's Address
Mike Amundsen
EMail: [email protected]
URI: <a href="http://amundsen.com">http://amundsen.com</a>
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