Semantic Web Publishing with RDFa

How you can use RDFa to embed structured content into your Web page and be part of the Semantic Web.
Publishing Tools

Tools are emerging from the RDF world at an accelerating pace this year, and you may find what you need without writing a line of code. Not all of them produce RDFa, however. Some, such as Semantic MediaWiki, produce the HTML and RDF side by side, from an internal triple store. It's a fair chance you've already used RSS (which originally stood for RDF Site Summary when it was created at Netscape back in 1999). If you use version 1.0, take a look at the RSS source—it's valid RDF/XML.

Another group to keep an eye on is the Simile Project at MIT. It has an interesting range of tools with the broad purpose of managing and reusing bits of digital data. Not all are RDF-related, but the RDFizer promises to convert a variety of structured formats to RDF for you: mbox, Debian software packages, Subversion and many more.

The most advanced tools probably are not yet in the open-source arena. Metatomix, Inc., has done some heavy lifting in the semantic application field, with major implementations in engineering, finance and integrated justice. I talked to CTO Howard Greenblatt, and he explained the company's technology stack. The key components are first, a set of development tools for creating the ontology, and second, a messaging platform that gathers data from traditional data sources and integrates it into a triple store, along with some business rules logic. For the first component, they have their own plugin for the Eclipse development environment, and for the second, they use Jena from HP Labs plus a bunch of proprietary code. Then, the whole thing can be queried in SPARQL, the query language of the Semantic Web.

That's more than most Web developers are likely to bite off. However, it brings us back to a point from our example above: choosing, or creating, an appropriate vocabulary. To say anything on the Semantic Web, you have to have a namespace in which to speak precisely. Writing your own vocabulary is not too hard (and Semantic MediaWiki helps you do it automatically), but you may want to choose a standard one, at least if you are interested in search engine discovery.

Search Engines and Vocabularies

Yahoo announced in March 2008 that it would start supporting Semantic Web standards, including microformats, RDFa and eRDF. And, it announced specific vocabulary components that would be supported: Dublin Core, Creative Commons, FOAF, GeoRSS and MediaRSS. Using these vocabularies will make your data more portable and easier for search engines to index intelligently.

If you want to see what vocabularies others are using, the GetN3 bookmarklet is helpful. A visit to, run through the GetN3 bookmarklet, shows that Digg is now embedding RDFa using the Dublin Core and Creative Commons vocabularies (prefixes added):

 cc:attributionName "Digg users";
 cc:license cclicense:publicdomain/;
 dc:source <>;
 dc:title "Jules Verne in Orbit";
 dc:abstract "The bright edge of planet Earth..";
 dc:creator <>;
 dc:date "2008-04-05 05:07:38";

I think the Semantic Web is finally taking off this year. Semantic applications range from personal desktop productivity (MIT's Piggybank) to new Web search engines (Yahoo) to huge enterprise applications and even military information-sharing. As the social networks grow heavy with data, sharing and structuring that data becomes more important. Eric Miller, an MIT professor who led the Semantic Web initiative for the W3C, sees “a new market space for data aggregation, data integration, and data discovery”. And, all you have to do to be a part of that space is add a couple tags into your page.


Thanks to the following individuals for their time, assistance and insight: Michael Hausenblas, Ivan Herman, Eric Miller, Howard Greenblatt, Duane Degler, Marwan Sabbouh and Michel Biezunski.

Golda Velez ( is a developer, consultant and freelance writer focusing on emerging technologies. She works on developing vocabularies for specialized domains and partnering with domain experts to create vertical sites. She lives with her husband and children in Tucson, Arizona.