Suppose I have a bunch of words.
Certain words are "under" other words
or "related" to other words. I need a
good way to group them and know their
relationship.
Take a look at wordnet, which is available in RDF format i.e. according to an RDF Schema ontology. This is exactly what you describe.
http://www.w3.org/2006/03/wn/wn20/
(C. Fellbaum. WordNet: An Electronic Lexical Database. MIT Press, 1998. See also http://wordnet.princeton.edu/ )
(van Assem, Gangemi and Schreiber (eds.). RDF/OWL Representation of WordNet, W3C Working Draft 19 June 2006 W3C Working Draft 19 June 2006; http://www.w3.org/TR/2006/WD-wordnet-rdf-20060619/)
