Do you write HTML? You’ve just heard that Google now supports RDFa and you want to know where to start? Our own Steven Pemberton just published a fantastic RDFa introduction for HTML authors:
RDFa is a thin layer of markup you can add to your web pages that makes them understandable for machines as well as people. You could describe it as a CSS for meaning. By adding it, browsers, search engines, and other software can understand more about the pages, and in so doing offer more services or better results for the user. For instance, if a browser knows that a page is about an event such as a conference, it can offer to add it to your calendar, show it on a map, locate hotels or flights, or any number of other things.
Mark Birbeck recently gave a Tech Talk at Google on the subject of RDFa. The talk begins with a detailed introduction to RDFa, and then looks at how RDFa can play a role in improving search, as well as enhancing the way that users can view information. A video of the talk is now available online.
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.)
We’ve reached a point where new editors’ drafts of the syntax and processing document, and an introductory primer are available, ready to be reviewed by the W3C’s Semantic Web Deployment Group at their next face-to-face meeting.
Take a look. RDFa is pretty close to completion…and now the fun can really begin.
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.
Fresh from the Semantic Web Activity News: GRDDL is a W3C Recommendation.
As you might know, GRDDL can also be used to generate RDF from XHTML+RDFa documents. However, there are people around preferring to use RDFa rather directly 
What can I say…this post has everything.
First, it shows how Egon has used RDFa to mark-up HTML documents with information about molecules–something he started doing last year. But then it shows how he uses the latest version of Operator (0.8) to parse the RDFa, and generate menus which will search chemistry databases.
What’s most interesting about this post for me, is that Egon actually went through the process of doing all of this by using a GreaseMonkey script first, before he then used Operator to do the heavy lifting. GreaseMonkey is great for general purpose processing on a page, but the important thing about extensions like Operator is that they deal with your page at the semantic level. It then makes it very easy to do the type of thing that Egon has done, and add a menu item that searches a specific database. By talking us through the ‘long-hand’ technique we start to see the real benefits of Operator.
I’m looking forward to the next instalment, because I think Egon’s on a roll here!
And once more Bob DuCharme has written an exquisite article, published by IBM developerWorks, called Put XHTML 2 to work now. To sum up the main idea of the article:
Many publishers that store content in XML have always known that using an existing, standard schema (by which I mean a W3C Schema, a RELAX NG schema, or a DTD) was better than creating their own from scratch. They looked at DocBook and found it too complex; they looked at HTML or XHTML 1 and found it too simple. For many of them, XHTML 2 will hit a sweet spot between the richness of DocBook and the simplicity of XHTML 1 that makes it a perfectly good format for storing content, whether that content has to be converted to other formats for delivery in various media or not.
What I liked best? The section Easier addition of metadata, where he writes about RDFa
Bob DuCharme has now written the second part of his excellent RDFa introduction. Bob explains data typing with RDFa, the usage of CURIEs, and other useful stuff. In the last section of this article, Bob discusses the template-based generation of RDFa; see also the blog entry on RDFa in Movable Type, and the FOAFr.
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.
