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owl:allValuesFrom and rdfs:domain

From: Bernard Vatant <bernard.vatant@mondeca.com>
Date: Thu, 18 Dec 2003 10:38:23 +0100
To: "Www-Rdf-Logic@W3. Org" <www-rdf-logic@w3.org>
Message-ID: <GOEIKOOAMJONEFCANOKCCEALCOAA.bernard.vatant@mondeca.com>


I need some help from experts in logic ...

I've sent a few days ago a message about "TexasThings" example in OWL Guide
(see below), where the interpretation of allValuesFrom seems wrong to me.
Without answer so far from there, I push the question here.

Suppose I have the following - more enlightening to me at least than Texas
Things :))

<owl:Class rdf:ID="BlueThing">
  <owl:equivalentClass>
    <owl:Restriction>
      <owl:onProperty rdf:resource="#color" />
      <owl:allValuesFrom rdf:resource="#ShadeOfBlue" />
    </owl:Restriction>
  </owl:equivalentClass>
</owl:Class>

<owl:ObjectProperty rdf:ID="color">
  <rdfs:domain rdf:resource="#VisibleThing"/>
</owl:ObjectProperty>

What can be asserted between the classes BlueThing and VisibleThing ?

Of course, if some BlueThing X has a value for "#color", then X is in the
domain of "#color". But using "allValuesFrom" means that some other
BlueThing Y may not have any value at all for this property.
How can this happen? Quite naturally, if Y is not a VisibleThing one might
not be able to specify any value for its color. One knows somehow Y is a
BlueThing, without being able to specify any ShadeOfBlue.

So a BlueThing is not necessarily a VisibleThing.

There is more tricky.

<owl:Class rdf:ID="InvisibleThing">
  <owl:complementOf>
    <owl:Class rdf:about="#VisibleObject"/>
  </owl:complementOf>
</owl:Class>

Does the following triple hold?

InvisibleThing  rdfs:subClassOf  BlueThing

Sounds weird ... but I can't find any solid argument against it.

Bernard

Bernard Vatant
Senior Consultant
Knowledge Engineering
Mondeca - www.mondeca.com
bernard.vatant@mondeca.com


-----Message d'origine-----
Envoye : lundi 15 decembre 2003 19:21
A : public-webont-comments@w3.org
Objet : TexasThings and owl:equivalentClass

Seems to me that there is something wrong, or at least misleading with the
example of "TexasThings"
http://www.w3.org/TR/owl-guide/#equivalentClass1

<owl:Class rdf:ID="TexasThings">
  <owl:equivalentClass>
    <owl:Restriction>
      <owl:onProperty rdf:resource="#locatedIn" />
      <owl:allValuesFrom rdf:resource="#TexasRegion" />
    </owl:Restriction>
  </owl:equivalentClass>
</owl:Class>

First it would certainly be better to have the singular "TexasThing" rather
than plural "TexasThings" :)

"TexasThings are exactly those things located in the Texas region ..."

This is obviously wrong. There is an allValuesFrom, but not a
someValuesFrom here. As defined, it means : If TexasThings are located
somewhere, they are located in Texas region.

An further on

" ... The difference between using owl:equivalentClass here and using
rdfs:subClassOf is the difference between a necessary condition and a
necessary and sufficient condition. With subClassOf, things that are
located in Texas are not necessarily TexasThings. But, using
owl:equivalentClass, if something is located in Texas, then it must be in
the class of TexasThings."

... but not the other way round, unfortunately.

In fact under this definition any thing located nowhere is a Texas Thing.
Thinking about it, maybe it makes sense after all. Nowhere is indeed in
Texas, and especially its middle ... :))
Received on Thursday, 18 December 2003 04:45:35 GMT

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