- From: Richard H. McCullough <rhm@PioneerCA.com>
- Date: Wed, 7 Mar 2007 14:21:40 -0800
- To: "Michael Schneider" <m_schnei@gmx.de>
- Cc: <bparsia@cs.man.ac.uk>, <matthew.williams@cancer.org.uk>, <semantic-web@w3.org>, <public-owl-dev@w3.org>
I'm not saying that disjointness is assumed, I'm saying that disjointness is a fact. In real-world concept formation, all species of a genus are mutually exclusive and mutually exhaustive. I don't know what terminology you use. Perhaps you would call this a taxonomy, instead of an ontology. I consider non-disjointness to be "bad", because that means that units in the intersection have multiple genii -- which means you are mixing together two different definitions (contexts) for these units. Dick McCullough mKE do enhance od "Real Intelligence" done; knowledge := man do identify od existent done; knowledge haspart proposition list; http://mKRmKE.org/ ----- Original Message ----- From: "Michael Schneider" <m_schnei@gmx.de> To: <rhm@PioneerCA.com> Cc: <bparsia@cs.man.ac.uk>; <matthew.williams@cancer.org.uk>; <semantic-web@w3.org>; <public-owl-dev@w3.org> Sent: Wednesday, March 07, 2007 6:22 AM Subject: Re: Question on DL negation > Hi, Dick! > > Richard H. McCullough wrote on Tue, 6 Mar 2007: > >> Your BTW3 really intrigues me. You say that "disjointness" increases the >> "complexity" of a DL, presumably a "bad" thing. > > I wrote: > >>> BTW3: I cannot see a feature "disjointness", neither for concepts, nor >>> for roles. Doesn't the addition of disjointness adds significantly to >>> the complexity of a DL? I thought that at least it would, when adding >>> concept disjointness to OWL-Lite. Or can disjointness be expressed in >>> terms of the other mentioned features? At least, I do not see how this >>> were possible for /role/ disjointness, when only having the features of >>> OWL1.0. > > By "complexity", I really meant /computational/ complexity, in the sense > of: > > http://en.wikipedia.org/wiki/Computational_complexity_theory > > This is a general runtime (or space) measure for a given computational > problem. > > The complexity navigator at > > http://www.cs.man.ac.uk/~ezolin/logic/complexity.html > > which Bijan pointed me to, shows the computational complexity (if already > known) for the (computational) problem of deciding, if a given ontology is > satisfiable or not. You can choose the different language features of the > description logic you are interested in, and then you can see how the > complexity class changes. > > Adding some language feature to a given language, for instance the feature > "class disjointness" to OWL-Lite, always has the /potential/ to increase > the computational complexity of the satisfiability problem, because every > reasoner for the augmented language (OWL-Lite+disj) now has to solve this > problem for all possible ontologies of the old language (OWL-Lite) PLUS > all those ontologies which contain the additional language feature > (disjointness axioms). But such an increase in complexity doesn't always > happen, I just /supposed/ that this was the case for the step from > OWL-Lite to OWL-Lite+disjointness. > > Unluckily, I cannot check this with the navigator, because there is no > such "concept disjointness" checkbox. It seems that all I can do is > comparing the complexity classes of OWL-Lite and OWL-DL, which is an > upper-language of OWL-Lite+disj: > > * Complexity( OWL-Lite ) = ExpTime (complete) > * Complexity( OWL-DL ) = NExpTime (complete) > > And according to > > http://en.wikipedia.org/wiki/EXPTIME > > it is currently unknown if ExpTime and NExpTime are different or not (most > probably different, so this approach does not really provide me much > help). > > Anyway, you see now that I had a very specific (and very technical) notion > of "complexity" in mind. > >> In real-world concept formation, all species of a genus are disjoint, >> and I believe this is a "good" thing -- a major factor contributing to >> the >> "simplicity" and the "power"of hierarchical classification. >> Perhaps it's only partial disjointness that is "bad"? >> I consider any intersection between species to be "bad". > > But you can use DLs like OWL to model whatever you want, not only "natural > species". And when comparing two general concepts, you cannot simply > assume disjointness (it would often be wrong), you instead have to > explicitly demand it, by adding a disjointness axiom. But, perhaps, I > misunderstood, what you meant here? > > Cheers, > Michael > >
Received on Wednesday, 7 March 2007 22:22:46 UTC