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RE: class and inviduals

From: Michael Schneider <schneid@fzi.de>
Date: Thu, 18 Nov 2010 09:04:16 +0100
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A00235B0D1@judith.fzi.de>
To: "Rinke Hoekstra" <hoekstra@few.vu.nl>, "Pavel Klinov" <pklinov@cs.man.ac.uk>
Cc: <public-owl-dev@w3.org>, "Pat Hayes" <phayes@ihmc.us>, "Marco Colombetti" <colombet@elet.polimi.it>
Hi!

Some more observations below!

>-----Original Message-----
>From: public-owl-dev-request@w3.org [mailto:public-owl-dev-
>request@w3.org] On Behalf Of Michael Schneider
>Sent: Thursday, November 18, 2010 12:28 AM
>To: Rinke Hoekstra; Pavel Klinov
>Cc: public-owl-dev@w3.org; Pat Hayes; Marco Colombetti
>Subject: RE: class and inviduals
>
>Hi again!
>
>I wrote earlier this day:
>
>>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!
>
>To make sure that this example is not just an "outlier", I did
>some more checking by using the SPARQL endpoint to DBPedia at
>
>    <http://dbpedia.org/sparql>
>
>with the following queries:
>
>Query 1:
>"""
>SELECT DISTINCT ?c
>WHERE {
>  ?c owl:sameAs ?d .
>  ?x rdf:type ?c .
>}
>"""
>
>Query 2:
>"""
>SELECT DISTINCT ?d
>WHERE {
>  ?c owl:sameAs ?d .
>  ?x rdf:type ?d .
>}
>"""
>
>Query 3:
>"""
>SELECT DISTINCT ?c, ?x
>WHERE {
>  ?c owl:sameAs ?d .
>  ?x rdf:type ?c .
>}
>"""
>
>Query 1 asks for all DBPedia concepts having rdf:type-based
>instances in the DBPedia knowledge base and for which there
>is an owl:sameAs-link to some other concept (not necessarily
>from DBPedia). Query 2 differs from Query 1 in that the
>concepts having rdf:type-instances are being owl:sameAs'ed
>from DBPedia concepts, but might not be DBPedia concepts
>themselves. So these two queries ask for concepts (internal
>or external to DBPedia) that are used dually as classes (via
>rdf:type) and individuals (via owl:sameAs) within DBPedia.
>Query 3 is like Query 1, but also asks for the instances
>of the identified dual-use concepts.
>
>Results: Query 1 returned 133 concepts, all of them being
>classes from the dbpedia-owl ontology. Query 2 returned
>1061 hits, all of them happened to be concepts from OpenCyc.
>Query 3 returned exactly 2000 hits, which is probably due
>to an internal result set restriction of the query endpoint.
>A closer look revealed that all returned instances belonged
>to the same dual-use concept, namely the first concept
>being returned by Query 1 ("dbpedia-owl:Actor"). So the true
>size of the result set for Query 3 is probably much larger.
>
>To summarize, DBPedia "puns" at least ca. 1200 concepts,
>and these dual-use concepts have at least 2000 instances,
>probably much more. I think this strengthens my earlier
>claim that the existing semantic difference between OWL 2 DL
>punning and RDF(S)/OWL-Full "true" metamodeling is practically
>sensible, since for each instance of a dual-use concept
>OWL Full will allow to infer a second instance relationship,
>which is not provided by OWL 2 DL reasoning. It would be
>interesting to extend this investigation in a more
>sophisticated way (e.g. not only using owl:sameAs-links)
>to a much larger fraction of the whole LOD cloud.

Having had a closer look at dbpedia-owl:Actor
(http://dbpedia.org/ontology/Actor),
which, as said above, has a large number of instances and
for which there is a owl:sameAs-link to opencyc:actor,
I could see that this concept is used in DBPedia as:
  (i) a sub-class of dbpedia-owl:Artist;
  (ii) a super-class of concepts, s.a. dbpedia-owl:VoiceActor;
  (iii) the domain of properties, s.a. dbpedia-owl:geminiAward.
Again, the difference between OWL 2 DL punning and 
RDF(S)/OWL-Full metamodeling will be sensible, since in 
OWL 2 Full one will be able to infer corresponding 
(i) sub-class-, (ii) super-class-, and (iii) domain relationships 
also for opencyc:actor, which are not entailed in OWL 2 DL.

I also found that OpenCyc maintains a rich multi-level 
metaclass hierarchy. For example, opencyc:actor 
(http://sw.opencyc.org/concept/Mx4rvVjaHZwpEbGdrcN5Y29ycA)
is defined as an instance of opencyc:type_of_entertainer
(http://sw.opencyc.org/concept/Mx4rvxw_ApwpEbGdrcN5Y29ycA).
The latter contains many other instances, such as
opencyc:magician, opencyc:DJ and opencyc:clown,
all of them having instances themselves, e.g. 
David Copperfield, D.J. Yella, and Herschel Krustofsky,
respectively. 
Further, the metaclass opencyc:type_of_entertainer is itself 
an instance of opencyc:faceting_collection_type
(http://sw.opencyc.org/concept/Mx4rvprlOZwpEbGdrcN5Y29ycA),
which again is an instance of opencyc:type_of_collection_type
(http://sw.opencyc.org/concept/Mx4rviPYH5wpEbGdrcN5Y29ycA).
Interestingly, the latter concept is defined as an instance 
of itself, resembling the rdfs:Class/owl:Class loops in 
RDFS and OWL Full.

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 Thursday, 18 November 2010 08:04:53 GMT

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