Bridging the Gap between RDF and XML

"It is a goal to facilitate the use of RDF mechanisms to access the information contained in a broad range of  XML documents, including those that were not initially structured according to the RDF 1.0 layering."

--- The Cambridge Communiqué [CC99]

Introduction

1. The semantics of XML documents can be made explicit. Both structural and semantic markup can coexist in the same document.
2. RDF can be used to annotate existing XML documents.
3. "RDF-enabled" XML can still be rendered and transformed using XSLT [XSLT99].
4. Using small changes in XML DTDs, meaningful RDF documents can be produced from original XML documents. But every XML document (even those without DTDs) has a default RDF interpretation.

Example

<?xml version="1.0">

<document>

  <title>Bridging the Gap between RDF and XML</title>
  <author>Sergey Melnik</author>

  <abstract>A proposal to provide RDF interpretation for XML</abstract>

  <section caption="Introduction">

     <p>The goal of this proposal is to facilitate the use of RDF mechanisms
        to access the information contained in a broad range of XML documents.</p>

     <p>It builds upon a <a href="syntax.html">simplified syntax</a> for RDF,
        but has a <em>broader</em> scope.</p>

  </section>

</document>

The following figure illustrates a possible semantic interpretation for this XML document:

An RDF parser needs some hints in order to determine whether a given XML element identifies a name of a relationship, or rather a class name. Every XML tag is regarded as a relationship name, unless an RDF property rdf:instance is used to override this default. To illustrate, we could add rdf:instance to the section tag in the above example to make a section to be an instance of the class "section". These hints can be stored in the DTD of the document without modifying the document content (see example).

The RDF interpretation of a document is controlled by the RDF tags rdf:instance, rdf:for and rdf:resource (compare [SM99]).

Instead of discussing the details of the XML-to-RDF mapping, the reader is encouraged to download the parser together with an RDF API and to experiment with it.

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References