This could be a big step toward the “web of data” vision of the Semantic Web.

Yahoo announced (Accessing Structured Data using BOSS that their BOSS (Build your Own Search System) will now support structured data, including RDF.

“Yahoo! Search BOSS provides access to structured data acquired through SearchMonkey. Currently, we are only exposing data that has been semantically marked up and subsequently acquired by the Yahoo! Web Crawler. In the near future, we will also expose structured data shared with us in SearchMonkey data feeds. In both cases, we will respect site owner requests to opt-out of structured data sharing through BOSS.”

Here’s how it works:

• Sites use microformats or RDF (encoded using RDFa or eRDF) to add structured data to their pages
• Yahoo’s web crawler encounters embedded markup and indexes the structured data along with the unstructured text
• A BOSS developer specifies “view=searchmonkey_rdf” or “view=searchmonkey_feed” in API requests
• BOSS’s response returns the structured data via either XML or JSON

Yahoo’s SearchMonkey only acquires structured data using certain microformats or RDF vocabularies. The microformats supported are hAtom, hCalendar, hCard, hReview, XFN, Geo, rel-tag and adr. RDF vocabularies handled include Dublin Core, FOAF, SIOC, and “other supported vocabularies”. See the appendix on vocabularies in Yahoo’s SearchMonkey Guide for a full list and more information.

A post on the Yahoo search blog also talks about this and other changes to the BOSS service and includes a nice example of the use of structured data encoded using microformats from President Obama’s LinkedIn page.

The W3C has officially announced that RDFa is a candidate recommendation

“2008-06-20: The Semantic Web Deployment Working Group has published a Candidate Recommendation of RDFa in XHTML: Syntax and Processing. Web documents contain significant amounts of structured data, which is largely unavailable to tools and applications. When publishers can express this data more completely, and when tools can read it, a new world of user functionality becomes available, letting users transfer structured data between applications and web sites, and allowing browsing applications to improve the user experience. RDFa is a specification for attributes to be used with languages such as HTML and XHTML to express structured data. See the group’s RDFa implementation report. The Working Group also updated the companion document RDFa Primer. Learn more about the Semantic Web and the HTML Activity.”

Achieving candidate recommendation status is a significant step toward becoming a W3C recommendation. Congratulation to the working group for all of their efforts in developing RDFa.