The Canonical Link Relation
RFC 6596
Document | Type |
RFC - Informational
(April 2012; No errata)
Was draft-ohye-canonical-link-relation (individual in app area)
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Authors | Maile Ohye , Joachim Kupke | ||
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 lostShow full document text