Bryan Lawrence had some thoughts on authoring RDFa in a Wiki. I’m quite excited to see this kind of development and looking forward seeing results in form of plug-ins, extensions, etc. - anyone else out there who has a concrete implementation available?
The Semantic Web Deployment Working Group and the XHTML 2 Working Group of the W3C have jointly published the Last Call Working Draft of RDFa in XHTML: Syntax and Processing. Comments are welcome through 21 March.
A couple of days ago, riese (RDFizing and Interlinking the EuroStat Data Set Effort) has been launched; it aims at serving the entire statistical data available via Eurostat (some 3 billion triple). Currently, riese is the largest known deployment of XHTML+RDFa content on the Web (some 5 million triple). In riese, several vocabularies are in use: From AtomOwl (for data updates) over DOAP (self-description of the project) to SKOS (hierarchical order of themes).
The riese Semantic Web application is a good-practice implementation of several of the Semantic Web Deployment WG, such as RDFa, SKOS, but also Best Practice Recipes for Publishing RDF Vocabularies (for riese’s schemas). Last but not least, riese is a contribution to the linked-data initiative, where the aim is to create semantic links between open datasets available on the Web.
So, congrats to Leo and Richard: Cool URIs for the Semantic Web is a W3C Working Draft, now. They basically discuss URI design issue regarding both humans and machines. Why do we care? Well, let’s have a look into the document:
The solutions described in the following apply to deployment scenarios in which the RDF data and the HTML data is served separately, such as a standalone RDF/XML document along with an HTML document. The metadata can also be embedded in HTML, using technologies such as RDFa [...], microformats and other documents to which the GRDDL [...] mechanisms can be applied. In those cases the RDF data is extracted from the returned HTML document.
What is your opinion? Do you have practical experiences — that is: no toy setup 
— in designing URIs in an XHTML+RDFa environment?
David Decraene is looking for feedback on his article Embedding OWL-RDFS syntax in XHTML with RDFa, which is a “Short introduction to RDFa, OWL and Microformats”, and aims to come up with:
a solution that reconciles the ease of use of Microformats with the expressivity of a language like OWL. Some problems hindering OWL adoptation will be highlighted, and a first experiment with the use of RDFa mark-up to embed OWL data directly into an XHTML page will be demonstrated, a solution that can be considered as a step higher than Microformats on the evolutionary ladder of the web.
He argues that OWL has a poor presence on the web, attributing this mainly to the fact that no-one has explored approaches to “align / integrate OWL with current web content”:
For ontological data to truly be useful, you need to somehow tie current web content with semantic classes and instances. OWL has failed miserably in this respect so far. It is much like a far away island of Eden, and a man without a canoe. All the important data could be there but no-one knows how to reach it. Granted, OWL does define a standard format for data interchange between applications, but this limited scope cannot be what the semantic vision is about.
Interestingly enough, if you replaced the word ‘OWL’ with the word ‘RDF’, you’d have pretty much the main motivations that spurred the development of RDFa in the first place. David goes on to give an example:
What we need is semantic annotation. You need to be able to tag sections of your content with explicit ontology classes and even relations, without it hindering the display of your content. If you wrote a piece on a certain bordeaux for example, you could mark up the section as being about an instance of wine, perhaps even with some properties defined (or even more amazing, just by knowing it is about wine properties can be extracted automatically, a mention of red is bound to be about the wine color).
Whilst there is no doubt that the kind of complex RDFa David uses in his post is not for the everyday user of RDFa, the fact that RDFa can be used for these kinds of complex examples shows that the architecture is solid.
(This rdfa.info post also appears on XForms and Internet Applications.)
A very interesting application of RDFa has been announced recently: Ontology Online. It is what I would call a Web 3.0 application, using the best of Web 2.0 and Semantic Web - check it out!
As Danny reported, it seems that Joost has triggered a race for using RDF in video metadata: ZDNet has reviewed the alpha version of Seesmic, an online video applications using RDF “as the foundation”, supporting vocabularies such as FOAF, SIOC, DC, MPEG-7 (cf. Multimedia Vocabularies on the Semantic Web report for further details). As an aside: Seesmic supports RDFa!
Kurt Cagle has a stunning article on RDFa, and interestingly enough draws attention to CURIEs as a key technology, since it formalises the use of scoped vocabularies.
I could draw attention to many interesting points, but one that particularly caught my eye was:
RDFa and Atom make for a surprisingly potent combination. One provides a useful way for annotating XHTML content with metadata easily and unobtrusively. The other provides a way of transporting both the metadata and its corresponding links such that generalized feed processors can display at least a minimal set of information about the given resource, and specialized feed processors can take the same Atom feed and use the object properties to generate considerably more sophisticated effects.
An excellent observation.
For anyone not familiar with Kurt’s work, it’s great to see him writing about RDFa. Kurt has a knack for being able to see the long term potential of new technologies, but at the same time explain to would-be users why such technologies could be useful to them.
He goes on:
Look for an upcoming article that will delve into the formal mechanics of building Atom feeds from RDFa and illustrating how you can extend certain CMS systems to better incorporate RDFa as a core capability.
I for one, am looking forward to that, and I think a lot of people will find those articles incredibly useful.
We started to gather applications on the Web that utilise RDFa. Have a look at the RDFa in the wild page and do not hesitate do contact us if you encounter a new Semantic Web application that uses RDFa (or maybe you want to announce your own?)
Thanks to Mike Kaply Operator 0.8 is now available. Operator is a Firefox plugin supporting all kinds of metadata in HTML (microformats, eRDF, RDFa). Try it out !