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RE: [OWLWG-COMMENT] Re: Cardinality Restrictions and Punning

From: Pat Hayes <phayes@ihmc.us>
Date: Sat, 22 Dec 2007 10:44:20 -0800
Message-Id: <p06230900c393066eb675@[]>
To: "Michael Schneider" <schneid@fzi.de>
Cc: "Jeremy Carroll" <jjc@hpl.hp.com>, "Owl Dev" <public-owl-dev@w3.org>

>Hi Pat!
>Pat Hayes wrote on Friday, December 21:
>>>Of course, the RDF compatible semantics for OWL-1.1 will have to be
>>>constructed in a way that the graph {(R1*)} becomes consistent.
>>I don't agree. One should expect that the Full semantics will support
>>more entailments than the DL semantics does, since the Full version
>>is obviously a more expressive language than the DL. A special case
>>of this is exactly the situation you describe, where an ontology
>>which is consistent in DL is inconsistent in Full.
>Then let's give OWL-1.1-Full unsatisfiable semantics, and everything will be
>fine. ;-)
>I don't think that it is a useful idea to allow OWL-DL-consistent ontologies
>to become inconsistent in OWL-Full.

I disagree. These are two distinct languages which differ profoundly 
in their basic methodology and semantics, one more expressive than 
the other and which has the less expressive language embedded into it 
as a proper subset. In fact, under these conditions it is almost 
inevitable that this will occur. Why would one not expect this? 
Obvious contradictions in quantified logic, such as

(forall (x)(= x a))
(not (= b a))

are consistent in propositional logic.

>And if this should not be preventable in
>general, one should at least take care that the cases for which this happens
>reduce to artificially looking "research examples".

Again I disagree. You may be being spooked by the word 
"inconsistent"; but as I am sure you know, this is simply another way 
to say that the more powerful language is able to prove entailments 
which are invisible to the less expressive language. So, sometimes 
there will be cases where a result is entailed in OWL-Full which is 
not entailed in OWL-DL. I don't find this at all a bad thing, or 
something to be avoided: on the contrary, this is often the chief 
motivation for wanting to use a more expressive language. And I am 
talking about real examples, not "research examples". Such as being 
able to infer, from the fact that a taxonomy represented as a class 
of classes contains only three members and that a thing is not in any 
of them, that it is not classified by the taxonomy.

>If I was an "ordinary"
>OWL ontology engineer, I would want to have a save feeling that my
>DL-consistent ontologies, which I have created by applying generally
>acknowledged design principles, will also be consistent under OWL-Full

If you are very attached to the "acknowledged design principles" that 
you are probably referring to (I do not such phrases seriously, 
myself) then indeed you should probably not be using the Full 
language. If on the other hand you are coming to this entire field 
without your intuition warped by the limitations of such 
"principles", the Full language is more likely to be of use to you.

>Otherwise I would become very skeptical about the practical value
>of OWL-Full (if I haven't been skeptical before anyway :)).

If one has lived all ones life in darkness, the light may seem harsh 
at first. :)

>Let's regard Jeremy's ontology discussed in my previous mail: If this
>ontology would have had different URIrefs for the data property eg:p and the
>object property eg:p, then Jeremy's example would have been a *very* simple
>and "naturally looking" ontology.


>For this "different-URI" version of
>Jeremy's ontology I certainly wouldn't have expected that it bites the dust
>in OWL-Full, and in fact with different names for the properties this
>ontology is actually OWL-Full *consistent*.

Quite. If one keeps a firm grasp of the basic idea that a name 
denotes a single thing, then everything is clear. Punning breaks that 
fundamental intuition.

>If a "little syntactical" property punning

I have never thought of punning as "little". Punning is a dangerous 
hack which is always liable to break. It is *inherently* fragile. 
Especially, as I tried to point out in an earlier message, when used 
to make a sort distinction invisible.  It is *inconsistent with 
equality*, which alone should be enough to be enough to make anyone 
acquainted with semantics seriously worried.

>  on the OWL-DL side leads to such
>big and unexpected semantical changes on the OWL-Full side, then something
>must be pretty wrong with the concept of data/object-property punning

I agree with that conclusion. I would strongly urge that the WG 
abandon this idea.

>>I would be more
>>worried if you could find an example the other way round.
>Perhaps, I will give it a try. But certainly not within the next few days.
>>This is the first I have heard of 'property punning'. Is there a
>>compelling use case for it? If not, I suggest dropping the idea.
>The only stated use case I remember at the moment was:
>     Evren Sirin (Wed, 05 Dec 2007):
>     "Punning object and data properties"
>     <http://lists.w3.org/Archives/Public/public-owl-wg/2007Dec/0061.html>
>On the other hand, IIRC, in the past, several WG members have considered
>property punning to be *not* very useful.
>Merry (semantic-free) Christmas!

I hereby officially shut down my semantic engine for 12 days.


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Received on Saturday, 22 December 2007 18:44:39 UTC

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