The Canonical Link Relation
RFC 6596
| Document | Type |
RFC - Informational
(April 2012; No errata)
Was draft-ohye-canonical-link-relation (individual in app area)
|
|
|---|---|---|---|
| Last updated | 2015-10-14 | ||
| Stream | IETF | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Reviews | |||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 6596 (Informational) | |
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Barry Leiba | ||
| Send notices to | stpeter@stpeter.im | ||
Internet Engineering Task Force (IETF) M. Ohye
Request for Comments: 6596 J. Kupke
Category: Informational April 2012
ISSN: 2070-1721
The Canonical Link Relation
Abstract
RFC 5988 specifies a way to define relationships between links on the
web. This document describes a new type of such a relationship,
"canonical", to designate an Internationalized Resource Identifier
(IRI) as preferred over resources with duplicative content.
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/rfc6596.
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.
Ohye & Kupke Informational [Page 1]
RFC 6596 The Canonical Link Relation April 2012
1. Introduction
The canonical link relation specifies the preferred IRI from
resources with duplicative content. Common implementations of the
canonical link relation are to specify the preferred version of an
IRI from duplicate pages created with the addition of IRI parameters
(e.g., session IDs) or to specify the single-page version as
preferred over the same content separated on multiple component
pages.
In regard to the link relation type, "canonical" can be described
informally as the author's preferred version of a resource. More
formally, the canonical link relation specifies the preferred IRI
from a set of resources that return the context IRI's content in
duplicated form. Once specified, applications such as search engines
can focus processing on the canonical, and references to the context
(referring) IRI can be updated to reference the target (canonical)
IRI.
2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. The Canonical Link Relation
The target (canonical) IRI MUST identify content that is either
duplicative or a superset of the content at the context (referring)
IRI. Authors who declare the canonical link relation ought to
anticipate that applications such as search engines can:
o Index content only from the target IRI (i.e., content from the
context IRIs will be likely disregarded as duplicative).
o Consolidate IRI properties, such as link popularity, to the target
IRI.
o Display the target IRI as the representative IRI.
The target (canonical) IRI MAY:
o Specify a relative IRI (see [RFC3986], Section 4.2).
o Be self-referential (context IRI identical to target IRI).
o Exist on a different hostname or domain.
Ohye & Kupke Informational [Page 2]
RFC 6596 The Canonical Link Relation April 2012
o Have different scheme names, such as "http" to "https" or "gopher"
to "ftp".
o Be a superset of the content at the context IRI.
* As an example, each component page (e.g., page-1.html, page-
2.html) of a multi-page article MAY specify the "view-all"
version (e.g., page-all.html), the superset of their content,
as the target IRI. This is because the content from each
component page is contained within the view-all version. Given
this implementation, applications can mark page-1.html and
page-2.html as duplicates of page-all.html, process content
only from page-all.html, and disregard the component pages.
All references can then be made to the view-all version (page-
all.html, the target IRI), and no content will have been lost
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