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Resource Directory Description Language (RDDL)

This version: January 3, 2001

Latest Version: January 3, 2001

Previous Version: January 2, 2001



This document defines Resource Directory Description Language (RDDL). A Resource Directory provides a text description of some class of resources and of other resources related to that class. It also contains a directory of links to these related resources. An example of a class of resources is that defined by an XML Namespace. Examples of such related resources include schemas, stylesheets, and executable code. A Resource Directory Description is designed to be suitable for service as the body of a resource returned by deferencing a URI serving as an XML Namespace name.

The Resource Directory Description Language is an extension of XHTML Basic 1.0 with a new element named resource. This element serves as an XLink to the referenced resource.

This document defines the syntax and semantics of the Resource Directory Description Language, and also serves as a Resource Directory Description for the namespace http://www.openhealth.org/RDDL/.

The Resource Directory Description 1.0 DTD has been produced as an extension of XHTML Basic 1.0 [5]. The definition uses the method described in Modularization for XHTML, based on the use of internal-subset parsed entities.


The Resource Directory Description Language was initially proposed and specified after discussion on the XML-DEV mailing list.

This document has no official standing and has not been considered nor approved by any organization.

The rddl:resource Element

The resource element is in a namespace whose name is http://www.openhealth.org/RDDL/. In this discussion, we assume the use of the namespace prefix rddl for this name, and refer to this element as rddl:resource.

The rddl:resource element represents a simple xlink (using the attributes defined in the XLink namespace), and an additional attribute content-type which provides for an optional content type specifier. The content-type attribute is not in any namespace.

The rddl:resource element is placed within the html body. The XHTML %Flow.mix entity has been redefined to contain rddl:resource so it roughly may be placed anywhere a p tag may be placed.

The rddl:resource element itself uses the %Flow.mix content model, and should have content which describes the associated resource.

<!ELEMENT rddl:resource (#PCDATA | %Flow.mix;)*>
<!ATTLIST rddl:resource
  xmlns:rddl		CDATA #FIXED 'http://www.openhealth.org/RDDL/'
  xlink:type	(simple)	#FIXED "simple"
  xlink:role	CDATA		'http://www.openhealth.org/RDDL/'
  xlink:arcrole CDATA		#REQUIRED
  xlink:title	CDATA		#IMPLIED
  xlink:href	CDATA		#IMPLIED
  content-type	CDATA		#IMPLIED

The definition above has been edited for clarity.



The value of this attribute must be supplied and must a URI reference. It provides a machine-readable identifier for the type of the related resource. Software perfoming resource resolution may dispatch on the this value.

It is anticipated that many related-resource types will be well known. A list of well-known resource types may be found at http://www.openhealth.org/RDDL/arcrole.htm (which itself is an RDDL directory).


The value of this attribute must be a URI reference. In this version of RDDL, its value must be the RDDL namespace name: http://www.openhealth.org/RDDL/.


This XLink locator attribute's value is a URI reference to the target related resource


A human readable short descriptive title. This should be specified but not be seen as a replacement for descriptive content.

xlink:show and xlink:actuate

Not used. The only legal value is "none".


An optional attribute whose value provides the related resource's media type. This attribute is not in any namespace.

Related Resources for RDDL

CSS Stylesheet

A CSS stylesheet used to provide the "look-and-feel" of this document, suitable in general for RDDL documents.


A DTD for RDDL, defined using Modularization for XHTML


  1. W3C XML Names
  2. IETF RFC 2396
  3. W3C XHTML 1.0
  4. W3C XLink
  5. W3C XHTML Basic 1.0
  6. W3C Note Harvesting RDF Statements from XLinks