Text will likely do what you are after. You can add themes and use the ABOUT function.
http://download.oracle.com/docs/cd/E11882_01/text.112/e10945/query.htm#i1006398Depending on how you set it up you can use the Fuzzy, stemming and/or soundex to help locate the results. You can also set up synonyms to even further refine the results.
For the little you mentioned about your exact requirements I would also look at the CTXRULE index to set up a classification system:
http://download.oracle.com/docs/cd/E11882_01/text.112/e10945/ind.htm#i1007378