XML News from Thursday, May 25, 2006

The W3C Semantic Web Best Practices and Deployment Working Group and HTML Working Groups have joined forces to publish RDFa Primer 1.0.

Current web pages, written in HTML, are chock-full of structured data. When publishers can express the document's metadata, and when tools can read it, a new world of user functionality becomes available, letting users copy and paste structured data between applications and web sites. An event on a web page can be directly imported into a user's desktop calendar. A license on a document can be automatically detected so that the user is informed of his rights automatically. A photo's creator, camera setting information, resolution, and topic can be published to enable structured search and sharing.

RDFa is a syntax for expressing such metadata in XHTML. The rendered, hypertext data of XHTML is reused by the RDFa markup, so that publishers don't repeat themselves. The underlying abstract metadata representation is RDF, which lets publishers build their own metadata vocabulary, extend others, and evolve their vocabulary with maximal interoperability over time. The metadata is closely tied to the data it describes, so that rendered data can be copied and pasted along with its relevant structure.

Here's asyntax example from the draft:

<h1 property="dc:title">Vacation in the South of France</h1>
  by <span property="dc:creator">Mark Birbeck</span>
  on <span property="dc:date" type="xsd:date"
    January 2nd, 2006

The thing that jumps out at me are the use of namespace prefixes in attribute values. Haven't we learned by now that this is a bad idea?