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This Version: February 14, 2003
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This document describes the Resource Directory Description Language (RDDL). A RDDL document, called a Resource Directory, provides a package of information about some target, including:
The Resource Directory Description Language is an extension of XHTML Basic
1.0 with two added attributes of the a element named
rddl:nature and rddl:purpose.
The Resource Directory Description Language was initially proposed and specified after discussion on the xml-dev mailing list. RDDL reflects contributions from many participants in the xml-dev mailing list
This document has no official standing and has not been considered nor approved by any organization.
a ElementA Resource Directory implements links to related resources
using the XHTML a element, enriched by two attributes in the
namespace identified by the URI http://www.rddl.org/
(identified in this discussion by the prefix rddl).
The attributes are named rddl:nature
and rddl:purpose, and an XHTML a element is
considered to be an entry in the resource directory if either or both of
these attributes are present.
Note that there is a rich assortment of other attributes defined by HTML
for the a element, to provide information about its title,
language, traversal and so on; their use is encouraged in Resource
Directories.
Related resources have a nature, a machine-readable label provided by
the value of the rddl:nature attribute.
For example, the nature of an XML Schema designed for use with a namespace
would be given as
rddl:nature="http://www.w3.org/2001/XMLSchema".
In cases where there is only one resource with a particular nature, the purpose of the linked resource may be inferred from this nature. For example, if there is only one related resource for a particular namespace whose nature indicates that it is a schema, processing software might infer that its purpose is to validate elements in that namespace.
The value of this attribute must be a URI reference, which must be converted to absolute form before being used. It provides a machine-readable identifier for the nature of the related resource. Software may dispatch on this value.
When the related resource is an XML language for which a namespace name has been defined, and for which the namespace name adequately distinguishes the nature of the resource, the namespace name should be used as its nature.
When the related resource is not an XML document but is adequately
distinguished by a MIME type, the value of the
rddl:nature attribute may reflect this MIME type with values
formed by the concatenation of the prefix
http://www.isi.edu/in-notes/iana/assignments/media-types/ with a
MIME type e.g.
http://www.isi.edu/in-notes/iana/assignments/media-types/text/css.
It is anticipated that many related-resource natures will be well known. A list of well-known natures may be found in the Resource Directory http://www.rddl.org/natures.
If a purpose but no nature is provided for a related resource, the default
value is
http://www.rddl.org/#resource.
Related resources may have a purpose, a machine-readable label
provided by
the value of the rddl:purpose attribute.
The purpose is designed to convey the intended usage of the related resource.
For example, two related resources might have natures that indicate they
are both schemas, but the purposes might indicate that one is designed to
validate the "strict" version of the language, the other the
"forgiving" form.
The value of this attribute must be a URI reference, which must be converted to absolute form before being used. It provides a machine-readable identifier for the purpose of the link to the related resource. Software may dispatch on this value.
It is anticipated that the purposes of many related resources will be well known. A list of well-known purposes may be found in the Resource Directory http://www.rddl.org/purposes.