SPARQL: Querying the Semantic Web

XML.com: Introducing SPARQL: Querying the Semantic Web: "This tutorial, the first of a three-part series, introduces SPARQL -- a query language and data access protocol for the Semantic Web. SPARQL is defined in terms of the W3C's RDF data model and will work for any data source that can be mapped into RDF. The specification is under development by the RDF Data Access Working Group (DAWG) and has recently reached Last Call Working Draft.

At this point in its life cycle the specification is stable enough that developers can begin seriously exploring its capabilities. And the availability of several SPARQL query engines means that this exploration can be practical rather than theoretical."