• Link - DBpedia.org: Querying Wikipedia like a Database

From the site:

DBpedia is a community effort to extract structured information from Wikipedia and to make this information available on the Web. DBpedia allows you to ask sophisticated queries against Wikipedia and to link other datasets on the Web to Wikipedia data.

Their demo page for the subject Semantic Web, using DBpedia's Linked Data Interface format.

Here's a raw query string for the Semantic Web, using a less structured interface for query results and casting with a wider net.

A fairly complete description of the DBpedia concept ( PDF ). From the document,

Another interesting approach is followed by Freebase [ link to Freebase ]. The project aims at building a huge online database which users can edit in a similar fashion as they edit Wikipedia articles today. The DBpedia community cooperates with Metaweb and we will interlink data from both sources once Freebase is public.