Internet Engineering Task Force (IETF) M. Amundsen

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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RFC 6573 The Item and Collection Link Relations April 2012

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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RFC 6573 The Item and Collection Link Relations April 2012

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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RFC 6573 The Item and Collection Link Relations April 2012

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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RFC 6573 The Item and Collection Link Relations April 2012

[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: [email protected]
URI: http://amundsen.com

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