Harry Chen from Image Matters LLC gave an invited lecture in Tim Finin’s semantic web class. His topic was an introduction to Geospatial Semantic Web technology. Harry discussed the problems related with unstructured geo-data and showed how to resolve some of the issues using RDFa.
Archive for March 2007
Kurt Cagle writes about the future of XML, and says a few very interesting things about RDFa:
Similarly, I suspect that while RDFa may have a fairly major hill to climb in terms of adoption, it will likely end up becoming integral to the semantic web fairly soon. Folk ontologies (or folksonomies, as some have referred to them) are not in fact really ontologies at all – they are instead simply property associations. If you can articulate a consisten property relationship using attributes outside of the normal XHTML ones, then you can do more than simply tag a document – you can in fact create relationships between entities in an XHTML document without having to leave the context of that document. That’s what RDFa does. These can then be interpreted by RDF enabled tools, making it possible to achieve something of the holy grail of the semantic web – provide a simple way of nonetheless encoding metadata into a document. I’ve argued for years that RDF as it exists right now is too complex for your average web developer, and what’s more it perforce requires duplication of content between the RDF and XHTML (or whatever document format you’re using). Eliminate this need for duplication by embedded the descriptive relational characteristics directly in the element’s attribute set, and all of a sudden the Semantic Web begins to move away from being unachievable to being doable.
Ivan Herman gave a comprehensive Tutorial on Semantic Web Technologies (incl. some nice slides regarding RDFa). Check it out!
RDFa started out as a project within the XHTML2 community. Oftentimes, people think that means it can’t work at all without XHTML2. Importantly, because RDFa is effectively only extra attributes in the body, you can start using RDFa right now in any version of HTML. You won’t “validate”, but you’ll still be “compliant” with the HTML specification, which says that extra attributes should just be ignored by the browser, and that’s exactly what happens.
That said, we want RDFa to be clean from a web architecture standpoint. In the words of Dan Connolly, that means that you should be able to “follow your nose” from a document that contains RDFa to a specification of RDFa. That’s why we’re building RDFa as an XHTML 1.1 module, so you’ll be able to specify that your page contains RDFa with a module declaration, and your document will validate. Importantly, the latest HTML Working Group charter of the W3C, now has an “encouragement for extensibility”:
The HTML WG is encouraged to provide a mechanism to permit
independently developed vocabularies such as
Internationalization Tag Set (ITS), Ruby, and RDFa to be mixed
into HTML documents. Whether this occurs through the
extensibility mechanism of XML, whether it is also allowed in
the classic HTML serialization, and whether it uses the DTD and
Schema modularization techniques, is for the HTML WG to
determine.
This means that, if the HTML WG does the right thing and follows this encouragement, we’ll also be able to make RDFa validate in HTML5. RDFa is, after all, just about agreeing on a few tweaks of syntax to enable interoperable structured data on the web. The really exciting stuff will be the applications, of course.
There’s a brand new version of the RDFa Primer just published as a working draft. If you want to dig into RDFa, that’s where you should start.
We’ve released new versions of the RDFa bookmarklets, including a revamped core RDFa Javascript library that supports multiple space-separated values in REL and CLASS, no longer produces triples for non-namespaced values, and doesn’t interfere with any existing Javascript prototypes. In passing, we’ve also released the RDFa Web Clipboard, which shows a bit of the potential power of RDFa: copy-and-pasted for all web data.
