google: rdf validator
google: rdf graphiviz
google: IsaViz
http://www.w3.org/2001/11/IsaViz/
google: jena
http://jena.sourceforge.net/

A Programmer's Introduction to RDQL
http://jena.sourceforge.net/tutorial/RDQL/index.html
SELECT ?x
WHERE (?x "John Smith")

google: rdf query.by.example
http://ilrt.org/discovery/2002/04/query/