State-of-the-Art of Ontology Languages

see e.g.  wikipedia

Not too helpful IMHO. First of all, we should not choose any language that is not used by any other user modeling ontology. Secondly, we have already collected some reasons why RDF-based ontology languages are a good choice for us (basically because of interlinking). Then, the listing of languages is not reliable at all; some comments:

• Cyc: the language is maybe not so interesting (Lisp-like; no open-source reasoner available), but the ontology is. It's an upper ontology. See  UMBEL for a reasonable integration of Cyc with the (semantic) web, which is actually used.
• Gellish: doesn't seem to be widely used on the web
• IDEF5: is not an ontology language, but an ontology engineering methodology.
• KIF: used to be important (is the original language of SUMO), but doesn't seem to be actively maintained or even advanced
• RIF:  the project has produced a lot of specifications but still is far away from practical applications and working implementations.
• OWL: OK, widely used for expressing things. Full reasoning support is rarely used in practice.

--Christoph