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Re: SEM: semantics for current proposal (why R disjoint V?) (sameState TEST)

From: Dan Connolly <connolly@w3.org>
Date: 29 Apr 2002 09:23:20 -0500
To: Ian Horrocks <horrocks@cs.man.ac.uk>
Cc: Pat Hayes <phayes@ai.uwf.edu>, www-webont-wg@w3.org
Message-Id: <1020090202.26978.28.camel@dirk>
On Sun, 2002-04-28 at 12:59, Ian Horrocks wrote:
> What you seem to want is to use datatype values as "keys", and I can
> see why this might be useful. 

Good; thanks.

> Unfortunately, the interaction of UnambiguousProperty and datatypes
> makes this problematical. Imagine, for example, that a datatype
> consisting of integers in the range 0-999 is used as a unique-id/key
> for instances of the class Person such that all persons have exactly
> one unique-id, all unique-ids are integers in the range 0-999, and
> unique-id is an UnambiguousProperty.  In order to function correctly,

That is: 'in order to function as Ian would like'. We don't
have a requirement for complete-and-tractible reasoning.

> a reasoner is now required to understand the properties of datatypes,
> e.g., that the cardinality of this particular datatype is 1,000, and
> that as a result no model can contain more than 1,000 instances of
> Person (note that this would not be the case if unique-ids were reals
> in the range 0-999). 
> 
> The formal properties of the resulting logic are not well understood
> (e.g., it is not clear yet if the language would be
> decidable). Moreover, it would cause severe problems for implementors

Implementors of complete reasoners, yes, I can see that.

But I'm having trouble seeing this as a problem users are likely
to run into in practice. If you could pose a test case that's
pretty clearly something folks want to do, that might help.

If this sort of class is a problem,
I'd prefer to limit cardinality constraints to
0/1/2/infinity than give up the sameState functionality.


> and might be a source (admittedly not the only possible source) of
> crippling intractability:

I don't find intractibility crippling at all.

> remember that, unlike a database, the
> existence of 2,000 individual names would not be an error, but would
> lead to the inference that the names must be partitioned into 1,000
> sets of "sameIndividuals". Check out the number of ways that 2,000
> elements can be partitioned into 1,000 sets - it is a big number!
> 
> This is an irresistible opportunity for a very nice citation [1] :-). 
> Sadly, Stirling does not seem to have made this work available on
> his web site.
> 
> Regards, Ian
> 
> [1] Stirling, J. Methodus differentialis, sive tractatus de summation
> et interpolation serierum infinitarium. London, 1730. English
> translation by Holliday, J. The Differential Method: A Treatise of the
> Summation and Interpolation of Infinite Series. 1749.
> 
> On April 23, Dan Connolly writes:
> > On Tue, 2002-04-23 at 17:23, Ian Horrocks wrote:
> > > On April 8, Pat Hayes writes:
> > [...]
> > > > so these issues seem largely irrelevant; whereas the inconvenience 
> > > > and artificiality of maintaining the restriction is a real barrier to 
> > > > deployment. There is no *semantic* reason for the distinction.
> > > 
> > > W.r.t. the domains, the interaction between the concept language and
> > > the built in datatype predicates is at best unpleasant and may even
> > > lead to undecidability (no definitive result at present). I also don't
> > > believe that this is "a real barrier to deployment" (can you show me
> > > examples where users really need objects that are both individuals and
> > > data values?).
> > 
> > Fair question. It comes up quite a bit in my work.
> > I don't make any claims about 'individuals'; but
> > I need to have UnambiguousProperty's that
> > take literal values.
> > 
> > For example, U.S. states that have the same 2-letter
> > postal code are the same state. So if I know
> > 
> >   :stateCode a ont:UnambiguousProperty.
> > 
> >   _:x :stateCode "KS".
> >   _:x :population "2688418".
> > 
> >   _:y :stateCode "KS".
> >   _:y :stateBird :WesternMeadowlark.
> > 
> > then I should be able to conclude
> > 
> >   _:z :population "2688418".
> >   _:z :stateBird :WesternMeadowlark.
> > 
> > 
> > Full details, with namespaces spelled out and all that, in:
> >   http://www.w3.org/2002/03owlt/sameStateP.rdf
> >   http://www.w3.org/2002/03owlt/sameStateC.rdf
> > 
> > 
> > > I believe that a much bigger barrier to deployment
> > > would be devising a language where complete (and perhaps even sound)
> > > reasoners were difficult or impossible to build.
> > 
> > Yes, well, we disagree on that.
> > Perhaps it belongs in the issues list? I don't see
> > it there.
> > 
> > http://www.w3.org/2001/sw/WebOnt/webont-issues.html
> > 
> > It is in the list of objectives.
> > 
> >   Effective decision procedure
> >   http://www.w3.org/TR/2002/WD-webont-req-20020307/#section-objectives
> > 
> > Perhaps that's enough? or perhaps each objective should
> > have a corresponding issue?
> > 
> > -- 
> > Dan Connolly, W3C http://www.w3.org/People/Connolly/
> > 
> > 
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Monday, 29 April 2002 10:23:05 GMT

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