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RE: class and inviduals

From: Michael Schneider <schneid@fzi.de>
Date: Thu, 18 Nov 2010 00:27:51 +0100
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A00235B0C9@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 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.

Best,
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 23:28:26 GMT

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