DL riddle

Yesterday we stumbled upon quite a hard description logics problem. At least I think it is hard. The question was, why is this ontology unsatisfiable? Just six axioms. The ontology is availbe in OWL RDF/XML, in PDF (created with the owl tools), and here in Abstract Syntax.

Class(Rigid complete restriction(subclassof allValuesFrom(complementOf(AntiRigid))))
Class(NonRigid partial)
DisjointClasses(NonRigid Rigid)
ObjectProperty(subclassof Transitive)
Individual(publishedMaterial type(NonRigid))
Individual(issue type(Rigid) value(subclassof publishedMaterial))

So, the question is, why is this ontology unsatisfiable? It is even a minimally unsatisfiable subset, actually, that means, remove any of the axioms and you get a satisfiable ontology. Maybe you like to use it to test your students. Or yourself. The debugger in SWOOP actually gave me the right hint, but it didn't offer the full explanation. I figured it out, after a few minutes of hard thinking (so, now you know how bad I am at DL).

Do you know? (I'll post the answer in the comments if no one else does in a few days)

(Just in case you wonder, this ontology is based on a the OntOWLClean ontology from Chris Welty, see his paper at FOIS2006 if you like more info)

Talk in Korea

If you're around this Tuesday, February 13th, in Seoul, come by the Semantic Web 2.0 conference. I had the honor to be invited to give a talk on the Semantic Wikipedia (where a lot is happening right now, I will blog about this when I come back from Korea, and when the stuff gets fixed).

Looking forward to see you there!

Mailproblems

The last two days my mail account had trouble. If you could not send something to me, sorry! Now it should work again.

Since it is hard to guess who tried to eMail me in the last two days (I guess three persons right), I hope to reach some this way.

Building knowledge together - extended

In case you did not notice yet -- the CKC2007 Workshop on Social and Collaborative Construction of Structured Knowledge at the WWW2007 got an extended deadline due to a number of requests. So, you have time to rework your submissions or finish yours! Also the demo submission deadline is upcoming. We want to have a shootout of the tools that have been created in the last few years, and get hands on to the differences, problems, and best ideas.

See you in Banff!