- From: Pat Hayes <phayes@ihmc.us>
- Date: Mon, 22 Oct 2007 15:56:33 -0500
- To: "Michael Schneider" <schneid@fzi.de>
- Cc: "Owl Dev" <public-owl-dev@w3.org>
>Hi! > >OWL-Full has ever been a complete mystery to me, .... .... It is really quite simple. Take OWL/RDF and think of it as an RDF 'extension'. The RDF and OWL vocabulary (and associated constructions) have to satisfy all the RDF and OWL semantic conditions stated in the specs. OK, that is all there is to OWL-Full. It does not constrain the form of an RDF graph and it does not impose any syntactic conditions on how the OWL vocabulary is used. It does however insist that however it gets used, the meanings of this vocabulary must satisfy the semantic conditions imposed upon it. It does not recognize distinctions like that between class/individual/property and between object/datatype classes or properties. In this, it follows RDF and RDFS, since the RDF semantics (and the ISO Common Logic semantics) allows any name to denote any 'type' of thing, or indeed to denote several of them at once. Notice that I did not mention the OWL 'abstract syntax' at all. At the insistence of the Manchester members of the working group, the OWL spec is stated with the abstract syntax as primary, and the mapping into RDF described almost as an afterthought, a 'projection' from the real language to an alien notation. This is not the right way to think about OWL-Full, and not how it was conceived. It is designed to fit into a picture where RDF is primary and more complex languages are created by adding special vocabularies to RDF with associated semantic conditions imposed on their meanings. This is how RDFS is described, for example, and OWL-Full is in the same tradition. In fact, OWL-Full was created in response to a claim made and reiterated several times in the WG, that a language as complex as OWL was inherently incompatible with RDF, and that the RDF encoding therefore should be abandoned. Echoes of that debate can still be heard in some parts of the world. This gives a rather different perspective to several contentious issues. From the Manchester view, some parts of OWL/RDF are genuine OWL assertions, while others are simply artifacts of the syntactic embedding from the abstract syntax. There is absolutely no such distinction in OWL-Full. Again, some RDF graphs are considered by DL thinkers to be 'assertions about the logical syntax' or to 'change the meaning of the logical syntax'; but neither claim is true when seen from the perspective of OWL Full itself. No OWL/RDF assertion can change the semantics of, say, rdf:type or of owl:Restriction, as these semantics are written into the semantic specification. What one can do is *add to* the meaning of such terms by imposing extra, axiomatically stated, conditions, ie by writing axioms. This can, in some cases, have some peculiar consequences; but they are not incoherent or illogical, just, well, peculiar. (OWL-DL also allows for some very peculiar conclusions arising from its insistence on extensional readings of classes and properties.) But it also allows for some very useful generalizations which have potential uses in real ontologies. Anyway, I hope this helps. Pat -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 cell phayesAT-SIGNihmc.us http://www.ihmc.us/users/phayes
Received on Monday, 22 October 2007 20:56:50 UTC