- From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
- Date: Mon, 22 Oct 2007 16:27:36 -0400 (EDT)
- To: schneid@fzi.de
- Cc: public-owl-dev@w3.org
From: "Michael Schneider" <schneid@fzi.de> Subject: Some basic questions about OWL-Full Date: Mon, 22 Oct 2007 22:06:40 +0200 > Hi! > > OWL-Full has ever been a complete mystery to me, and I admit that I have > never really made an approach to explore it. But now that people have > started to work on a new version of OWL, I think it is a good time for me to > at least try to learn a few fundamental facts. So dear OWL-Full experts: I > will put a few questions, all very basic, and all of them can be answered by > just saying "yes" or "no". But I won't bite you if you also add a small > explanation to each of your answers. :) > > (1) My first question is about syntactically correct OWL-Full ontologies. I > always thought that simply "everything" is allowed in OWL-Full. So my > question: Is every RDF graph an allowed OWL-Full ontology? Yes. Some RDF graphs make better OWL-Full ontologies than others, but they all are acceptable. > (2) The rest of my questions all deal with semantics. I think I have heard > somewhere that one can "change the semantics" of OWL-Full itself by stating > axioms about OWL vocabulary, but I don't know if this is true, and not even > what this exactly means. Ok, let's test this by creating a concrete example! > I would have said that the following two statements lead to inconsistency > even in OWL-Full: > > :x owl:sameAs :y . > :x owl:differentFrom :y . > > But what if I add the following axiom: > > EquivalentProperties(owl:sameAs owl:differentFrom) > > This should at least be syntactically ok in OWL-Full (see (1)). But have I > also managed to make this ontology semantically consistent with this trick? > I don't believe so, but I am also not certain. And whatever answer is > correct, I do not have an explanation for any of them. As OWL (even OWL Full) is monotonic, you can't make an inconsistent ontology consistent by adding more things to it. Note that :x owl:sameAs :y . EquivalentProperties(owl:sameAs owl:differentFrom) [actually a translation of it into an RDF graph, but let's ignore this detail] is inconsistent, as it says that the denotation of :x is equal to the denotation of :y (obviously) and *also* that the denotation of :x is not equal to the denotation of :y. For homework: Is EquivalentProperties(owl:sameAs owl:differentFrom) itself inconsisten? > (3) A more general question: Is it true that whenever an OWL-DL ontology is > inconsistent under OWL-DL semantics, then it is also inconsistent under > OWL-Full semantics? Would sound reasonable to me, but I am not sure. Yes, but not vice versa. (See theorem 2 in http://www.w3.org/TR/2004/REC-owl-semantics-20040210/rdfs.html.) > (4) Looking at both questions (2) and (3) brings me to my last question. The > ontology in question (2) is *not* an allowed OWL-DL ontology, of course, but > it contains a sub-ontology which is syntactically allowed in OWL-DL: The > first two statements above. So I ask if the following claim is true: "Given > [] an OWL-Full ontology [that] contains an OWL-DL sub-ontology [] which is > inconsistent under OWL-DL semantics, then the complete OWL-Full ontology is > inconsistent under OWL-Full semantics." Is this true or wrong? Yes, from just above and monotonicity. > Ok, I think that this is enough for me for the moment to get a first feeling > for OWL-Full. > > Cheers, > Michael Have fun, peter
Received on Monday, 22 October 2007 20:35:11 UTC