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Re: http://ld2sd.deri.org/lod-ng-tutorial/

From: Yves Raimond <yves.raimond@gmail.com>
Date: Tue, 23 Jun 2009 10:16:17 +0100
Message-ID: <82593ac00906230216t234da8d8m23d8bd602b42b1e2@mail.gmail.com>
To: Alan Ruttenberg <alanruttenberg@gmail.com>
Cc: hepp@ebusiness-unibw.org, martin.hepp@ebusiness-unibw.org, Michael Hausenblas <michael.hausenblas@deri.org>, Richard Cyganiak <richard@cyganiak.de>, "Hepp, Martin" <mhepp@computer.org>, Hugh Glaser <hg@ecs.soton.ac.uk>, mark.birbeck@webbackplane.com, "Booth, David (HP Software - Boston)" <dbooth@hp.com>, "public-lod@w3.org" <public-lod@w3.org>
Hello!


>> Hmm, I am still not sure I get it. What do you mean by 100% reliable?
>> Can you be more sure that following an owl:imports link will lead you
>> to something more reliable?
>
> It means that the full semantics of an OWL ontology is defined by a file and
> all the imports. Axioms that are not on the class directly, or even not on a
> superclass, might have an effect on inference. For example, one can write,
> in OWL
> As a simple example, one can write, in any import, EquivalentClasses(:a :b).
> If you don't get that bit, then you will miss important inferences. For a
> more complicated example you could have
> FunctionalObjectProperty(p)
> InverseFunctionalObjectProperty(p)
> ObjectPropertyDomain(:a)
> ObjectPropertyRange(:b)
> That p is functional and inversefunctional property forces that there be a
> one to one relationship between subject and
> object. So if we say that :b is an enumerated class
> EquivalentClasses(:b ObjectOneOf(:i1 :i2 :i3))
> and that every instance of :a is :p related to some :b
> SubClassOf(:a ObjectSomeValuesFrom(:p :b))
> Then that forces the class :a to have at most 3 members, because we've
> stated that every instance of :a has a :p relation to some :b, that :p is
> one to one, and there are at most 3 distinct individuals in :b. Each of the
> axioms in this example could conceivably be in a different imported file.
> Tracking down, for a given class, what is a smaller set of axioms than is
> included in the full imports tree, but still yields the same set of
> inferences, is known as "modularization".
>>
>> > Serving fragments of likely relevant parts of an ontology for reducing
>> > the
>> > network overhead is not the same as proper modularization of the
>> > ontology.
>>
>> But if the concise description of the term is sent back when you
>> dereference a term, you should be able to explore the whole ontology
>> (class to its subclass to the ontology it is defined in etc.) and
>> therefore commit to all the axioms in it if indeed you need to? How
>> would such mechanism be different than following an owl:imports link?
>
> As you see from above, it isn't trivial to decide which axioms you need. If
> you want to be guaranteed that, put into a reasoner, you will get the
> inferences that the author of the ontology intended, then absent an
> algorithm for doing modularization correctly (nontrivial), the only way is
> to take the whole import.
>


Thanks a lot for that! I think I understand now :-)

But does that mean *all* LOD data currently available is "wrong" from
an OWL perspective (even the bits not using owl:sameAs ;-) )? In the
RDF representation of a resource, you typically find RDF statements
linking to other resources, and one statement linking the resource to
its type. Should these statements be part of an owl:Ontology which
would import the ontology you want to commit to? Indeed, axioms that
are in the ontology might have implications on the classification of
that particular resource?

Cheers, and thanks again!
y
Received on Tuesday, 23 June 2009 09:16:54 UTC

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