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Re: class and inviduals

From: Pavel Klinov <pklinov@cs.man.ac.uk>
Date: Wed, 17 Nov 2010 16:21:31 +0000
Message-ID: <AANLkTi=GXRby+5Q9R1+hKnC3Y706mLZ3j_2+3GS4X8Ec@mail.gmail.com>
To: Michael Schneider <schneid@fzi.de>
Cc: Rinke Hoekstra <hoekstra@few.vu.nl>, public-owl-dev@w3.org, Pat Hayes <phayes@ihmc.us>, Marco Colombetti <colombet@elet.polimi.it>
On Wed, Nov 17, 2010 at 3:56 PM, Michael Schneider <schneid@fzi.de> wrote:
> Hi Rinke, Pavel!
> I have to admit that I did not exactly understand what Pavel meant here.
> Or was it meant that it would be confusing if for a class having a class
> property its /instances/ would not inherit that property? That's in fact
> also not in OWL Full! But I would never expect such inheritance from the
> class level to the instance level, at least not in general. The property
> belongs to the class, not to its instances. (However, if someone really
> wanted this behavior for a specific property :p, he could write in OWL 2
> Full: ":p owl:propertyChainAxiom ( rdf:type :p ) .")

Yeah, this is what I meant while I now 100% agree that this wasn't a
good example. I was merely trying to say that use of punning requires
understanding of the difference between properties of the class and
the properties of its instances. I have heard people talking about
"properties of the class" when those were just existential
restrictions (A subclassof p some B).

Your example at the bottom is a much better one.


>>Hm, but for all practical purposes they *are* the same thing, they are
>>just interpreted differently dependent on context.
> For individual/class punning, OWL 2 DL interprets the same name in one case
> as an individual of the domain of discourse, and in the other case as a
> subset of the domain of discourse. This is a big difference from a semantics
> point of view. Now, OWL 2 Full interprets both occurrences as individuals,
> in fact as the same individual. The only difference is that in the case of
> class usage, an additional feature of that individual is taken into account,
> namely its associated class extension, which is a subset of the domain of
> discourse. But one definitely talks about one and the same individual in
> both cases. And, as you can see in the example at the end of my post, this
> may indeed lead to practically sensible differences.
>>OWL 2 DL reasoners
>>may separate these contexts for efficiency purposes, but an RDFS/OWL 2
>>Full reasoner or RDF query engine won't.
> It's not only a matter of efficiency in the case of OWL 2 DL reasoners. They
> must not provide those inferences that you would expect from treating the
> two occurrences as the same thing, otherwise they would become unsound. See
> below for an example.
>>This is fine if you ask me... I have yet to come across a situation
>>where this potential confusion had any practical consequences.
> You can see the difference in the LOD cloud. For example, OpenCyc includes
> the concepts "country" and "England", where "England" is an instance of
> "country", and where "country" is asserted to be equal to DBPedia's
> "Country" concept (the equality link is being created in both knowledge
> bases):
>    opencyc:country owl:sameAs dbpedia:Country .
>    opencyc:England rdf:type opencyc:country .
> where
>    opencyc:country :=
> <http://sw.opencyc.org/concept/Mx4rvViIeZwpEbGdrcN5Y29ycA>
>    opencyc:England :=
> <http://sw.opencyc.org/concept/Mx4rvViWaZwpEbGdrcN5Y29ycA>
>    dbpedia:Country := <http://dbpedia.org/resource/Country>
> An OWL Full reasoner and many existing RDF rule reasoners (including all
> reasoners implementing the OWL 2 RL/RDF rules) will infer from the equality
> link that
>    opencyc:England rdf:type dbpedia:Country .
> holds. OWL 2 DL reasoners, on the other hand, must not infer this in order
> to avoid to become unsound. And, in fact, Pellet and Hermit correctly (from
> their perspective) classify this as a non-entailment.
> With owl:sameAs links being a big topic in the LOD world, I'd say this is a
> practically relevant difference!
> Cheers,
> Michael
> --
> Dipl.-Inform. Michael Schneider
> Research Scientist, Information Process Engineering (IPE)
> Tel  : +49-721-9654-726
> Fax  : +49-721-9654-727
> Email: michael.schneider@fzi.de
> WWW  : http://www.fzi.de/michael.schneider
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Received on Wednesday, 17 November 2010 16:22:04 UTC

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