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Versions: 00 01 02 RFC 6892

Network Working Group                                           E. Wilde
Internet-Draft                                           EMC Corporation
Intended status: Standards Track                      September 22, 2012
Expires: March 26, 2013


                   The 'describes' Link Relation Type
                     draft-wilde-describes-link-01

Abstract

   This specification defines the 'describes' link relation type that
   allows resource representations to indicate that they are describing
   another resource.  In contexts where applications want to associate
   described resources and description resources, and want to build
   services based on these associations, the 'describes' link relation
   type provides the opposite direction of the 'describedby' link
   relation type, which already is a registered link relation type.

Status of this Memo

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   This Internet-Draft will expire on March 26, 2013.

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
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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Resource Descriptions . . . . . . . . . . . . . . . . . . . . . 3
   4.  Use Case  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  Change Log  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     7.1.  From -00 to -01 . . . . . . . . . . . . . . . . . . . . . . 5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6
































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1.  Introduction

   Resources on the Web can be identified by any (registered) URI scheme
   and can be represented by any (registered) media type.  In many
   cases, applications establish specific (i.e., typed) relations
   between the resources they are concerned with, which can either be
   under their control, or controlled by another authority.  A common
   usage pattern for associating resources is to have resources which
   are descriptions of other resources.  This specification registers
   the 'describes' link relation, which allows applications to represent
   the fact that one resource is a description of another resource.

   RFC 5988 [1] "defines a framework for typed links that isn't specific
   to a particular serialisation or application.  It does so by
   redefining the link relation registry established by Atom to have a
   broader domain, and adding to it the relations that are defined by
   HTML."  This registration request intends to augment the link
   relation registry with a link relation that is the inverse of the
   already registered 'describedby' relation, so that links between
   described resources and describing resources can be represented in
   both directions.


2.  Terminology

   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 RFC 2119 [2].


3.  Resource Descriptions

   Associating resources with descriptions of these resources is a
   recurring pattern on the Web. The IANA link relation registry
   established by RFC 5988 [1] currently contains a 'describedby' link
   relation type, which has been registered by POWDER [3].  The
   definition given in that registration is as follows: "The
   relationship A 'describedby' B asserts that resource B provides a
   description of resource A. There are no constraints on the format or
   representation of either A or B, neither are there any further
   constraints on either resource."

   Since many scenarios using resource descriptions need to represent
   the fact that some resource describes a resource (the opposite of the
   'describedby' relation), this document registers a 'describes' link
   relation type.  Establishing a link A 'describes' B asserts that the
   resource identified by A is a description of the resource identified
   by B, without constraining in any way the identifiers being used for



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   A and B, and the media types for the representations being provided,
   when those identifiers are dereferenced.  Specifically, it is
   possible that identifiers A and/or B have no associated interaction
   method (they could be URNs, for example), but it still is valid to
   establish the A 'describes' B link.

   Another design freedom is to use "chains" of 'describes' (or
   'describedby') links, so that one resource is a description of
   another resource, which in turn is a description of yet another
   resource.  The "levels" of descriptions can go as deep as required by
   an application, and are not constrained by this specification.


4.  Use Case

   Starting from the POWDER document specifying the 'describedby' link
   relation [3], the use case for the 'describedby' link relation is
   that a described resource, such as a HTML Web page, can specify a
   link where clients can find a description of this resource.  While
   the 'describedby' link relation is defined to be independent of
   specific formats and representations, within the context of POWDER,
   the assumption is that the linked resources most often will provide
   an RDF-based description, for example providing metadata about a
   document's author and other provenance information.

   The 'describes' link relation allows servers hosting description
   resources to associate those description resources with the resources
   that they are describing.  In the RDF-oriented scenario of POWDER,
   this means that a service managing description resources would use
   'describes' links to represent the fact that the description
   resources it exposes provide some description of the described
   resource, very likely in some RDF representation.  However, since
   link relations are independent of resource formats or
   representations, such an association could also be made in other
   formats such as XML or JSON, allowing servers to use a single and
   consistent link relation to associate description resources with
   described resources.

   Generally speaking, the idea of the 'describes' relation is the same
   as the idea of the 'describedby' relation: to be independent of
   specific formats and representations of both described resources and
   description resources.  The 'describes' link relation (together with
   the already registered 'describedby' link relation) thus serves as a
   general foundation of how described resources and description
   resources can be associated.






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5.  IANA Considerations

   The link relation type below has been registered by IANA per Section
   6.2.1 of RFC 5988 [1]:

      Relation Name: describes

      Description: The relationship A 'describes' B asserts that
      resource A provides a description of resource B. There are no
      constraints on the format or representation of either A or B,
      neither are there any further constraints on either resource.

      Reference: [[ This document ]]

      Notes: This link relation type is intended to be the inverse of
      the already existing 'describedby' relation type, thus allowing
      links to be established from the describing resource to the
      described resource.


6.  Security Considerations

   Resource descriptions SHOULD never be treated as authoritative or
   exclusive without relying on additional mechanisms for trust and
   security.  Resources can have many (possible conflicting)
   descriptions, and the 'describes' link relation type makes no claim
   whatsoever about the authority of the party providing the association
   between the two resources, or about the authority of the party
   providing the description resource.  Before making any assumptions
   about the authority of the description resource (both the accuracy of
   the description contained in the description resource, and the
   authority to provide a description of the described resource),
   clients need a context that allows them to understand both the
   authority of the description itself, and the authority to establish
   the 'describes' relation.  Nobody can stop clients from providing
   misleading unauthorized and/or descriptions, and clients need to have
   both a security and trust framework to allow them to choose between
   trusted and untrusted descriptions.


7.  Change Log

   Note to RFC Editor: Please remove this section before publication.

7.1.  From -00 to -01






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   o  Added "Use Case" section (Section 4).

   o  Improved Security Considerations

   o  Minor textual improvements


8.  References

8.1.  Normative References

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

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119, March 1997.

8.2.  Informative References

   [3]  Archer, P., Smith, K., and A. Perego, "Protocol for Web
        Description Resources (POWDER): Description Resources", World
        Wide Web Consortium Recommendation REC-powder-dr-20090901,
        September 2009,
        <http://www.w3.org/TR/2009/REC-powder-dr-20090901/>.


Appendix A.  Acknowledgements

   Thanks for comments and suggestions provided by Mark Nottingham.


Author's Address

   Erik Wilde
   EMC Corporation
   6801 Koll Center Parkway
   Pleasanton, CA 94566
   U.S.A.

   Phone: +1-925-6006244
   Email: erik.wilde@emc.com
   URI:   http://dret.net/netdret/










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