The World Wide Web Consortium (W3C) have issued a Candidate Recommendation for OWL, The Web Ontology Language.
OWL is a language for defining structured Web-based ontologies that enables richer integration and interoperability of data across applications and systems. OWL is essentially a more meaningful and semantic extension to XML, RDF, and RDF Schema (RDF-S) and DAML+OIL.
OWL is represented in three sublanguages: OWL Lite, OWL DL, and OWL Full.
I had the opportunity of visiting the W3C Day talks the other day for the Evolve 2003 conference and it was interesting hearing first hand from people responsible for some of the new directions from W3C.
A summary of the speakers at Evolve W3C Day can be found here.