RDF in XHTML

Task Force Document 12 October 2004

This version:: TBD
$Revision: 1.2 $ on $Date: 2004/10/20 13:49:31 $ GMT by $Author: adida $
Latest version:: TBD
Previous version:: http://www.w3.org/2003/03/rdf-in-xml.html
Editors: Ben Adida <ben@mit.edu>

Abstract

This document defines the requirements and deliverables of the RDF-in-XHTML task force. The purpose of this task force is to enable the inclusion of RDF metadata in an XHTML document.

Status of this document

This document is a work-in-progress meant to lead to consensus on issues that face the taskforce.

Please send comments to this document to public-rdf-in-xhtml-tf@w3.org (publicly archived).

There is a long standing requirement to embed meta-data in an HTML document. One would think that this requirement could be satisfied by combining XHTML with RDF/XML using XML Namespaces and XML Schema, but this is not so. Instead, there are many nuanced technical issues and a series of problem statements, such as Tim Berners-Lee's RDF in XHTML (April 2002) and Dan Connolly's RDF in XHTML (March 2003), related proposals and analysis, such as Sean Palmer's exhaustive RDF in HTML (May 2002), and Joe Reagle's RDF in XHTML task force document (May 2003). Previous discussions failed to converge upon a solution. The goals of this document are to:

Identify the requirements and constraints for embedding RDF in XHTML.
Document a solution for satisfying those requirements.
Document the commitments and milestones necessary of each constituency to deliver the solution.

Scenarios and Constraints

The following scenarios and constraints have been presented as specific sources of requirements (beyond the more general references of the EmbeddingRDFinHTML Wikki):

FOAF: FOAF in XHTML Files, Dan Brickley
Trackback: Scenario: Trackbacks, Joseph Reagle
Dublin Core: Scenario: Dublin Core Dave Beckett
Creative Commons: Scenario: Creative Commons Ben Adida

Existing Partial Solutions

Dublin Core: Scenario: Dublin Core Dave Beckett. Dublin Core already mechanisms for encoding flat characteristics of the document in HTML meta elements.
XHTML2 MetaInformation Module: MetaInformation Module by the XHTML Working Group

Requirements

The requirements of this task are defined in large part by the needs of the Semantic Web Best Practices and Deployment Working Group.

Cross-Referencing Standards: The HTML standard SHOULD provide a normative reference to RDF
Embedding:
1. Expressivity: The solution MUST support arbitrary (rich) assertions.
2. Format
  1. The RDF SHOULD be serializable in an XHTML-specific manner
  2. The RDF may also be expressed as RDF/XML.
3. Syntactic/Semantic Integration: the solution MUST support the serialization of an RDF triple as a clickable/viewable link.
Authoring: the solution
1. MUST enable XHTML authors to:
  1. easily represent characters (such as those captures by MathML expressions and XHTML character entities)
  2. define arbitrary "entities" (as is presently permitted in XML with DTDs)
2. SHOULD enable RDF authors to author their RDF serialization by hand, if so desired.
Validation
1. The XHTML document: all XHTML elements MUST strictly validate against its XHTML definition but other elements MAY be ignored.
2. The RDF metadata: MUST be extractable to RDF/XML using GRDDL..
Compatibility:
1. SHOULD NOT be rendered by existing browsers when current browsers do not render it
2. SHOULD be rendered by existing browsers as clickable links when the RDF triple is meant to be rendered as such