OpenCalais is a semantic tagging toolkit that allows you to submit text to it for semantic querying. The toolkit allows you to extract meaning from webpages and content.
To use the public web service, post the URL-encoded license, content, and parameters to http://api.opencalais.com/enlighten/rest/. If successful, the response is an RDF/XML file. You can parse the file directly or import it into an RDF store.