Internet DRAFT - draft-wilde-describes-link
draft-wilde-describes-link
Network Working Group E. Wilde
Internet-Draft EMC Corporation
Intended status: Informational October 17, 2012
Expires: April 20, 2013
The 'describes' Link Relation Type
draft-wilde-describes-link-02
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 April 20, 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 -01 to -02 . . . . . . . . . . . . . . . . . . . . . . 5
7.2. From -00 to -01 . . . . . . . . . . . . . . . . . . . . . . 6
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 -01 to -02
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o Changed category from "Standard" to "Informational".
o Minor textual changes.
7.2. From -00 to -01
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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