RDFa Syntax Working Draft published

The W3C announced at the weekend the availability of a new working draft titled RDFa in XHTML: Syntax and Processing. The document has been produced jointly by the Semantic Web Deployment Working Group and the XHTML 2 Working Group.

I've tracked RDFa kinda intermittently (I (mostly) lurk on the RDF in XHTML Taskforce mailing list), but I haven't managed to keep up with recent developments in the syntax so need to look at this document in more detail.

RDFa occupies a similar space to the GRDDL recommendation that I mentioned a few weeks ago, in that RDFa provides another means of making RDF data available on the Web. Like GRDDL, RDFa is a generic solution, neutral of any particular RDF vocabulary, and focuses on defining a set of processing rules that can be used with any RDF vocabulary. Where RDFa differs quite substantially from GRDDL is that it defines a (XML-attribute-based) syntax for representing RDF triples. This current draft deals with the specific case of deploying that attribute-based syntax in the XHTML format (and indeed makes use of some existing XHTML attributes; see section 2.1), but the intent is that the approach can be generalised to other XML languages/formats - "RDFa can be easily imported into other XML-based markup languages" (section 1) - and I imagine that future documents will address the general cases in more detail.

The current draft is a syntax specification, so is a fairly technical document, but a Primer is also available, and that provides a more "scenario-oriented" discussion of possible uses of RDFa (I think at the moment the Primer document is still a pre-publication "Editor's Draft", so still work in progress and liable to change).

The movement of RDFa towards a stable W3C specification raises the question of, given the availability of microformats (at least some of which are already GRDDL-enabled, I think), the capacity to define a new GRDDL-able markup convention, existing generalised GRDDL-enabled conventions such as Embedded RDF, and now RDFa, which is the most appropriate method for embedding structured data in XHTML? And I'm not even going to attempt to offer a categorical answer, other than to say "It depends". ;-) A while ago, Benjamin Nowack offered a "calculator" which is designed to allow you to assign varying priorities to different features and then tots up a score for each on the basis of your choices. I think (but I'm not 100% sure for the case of RDFa) the features of the various options have remained more or less the same since that tool was created, so it may offer some food for thought - though it should be used as a guide rather than a source of a categorical answer! And it's worth reading the discussion in the comments on that post too.