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Re: CHAIR-NOTE: Defaults and etc.

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 25 Jan 2002 07:41:00 -0500
To: hendler@cs.umd.edu
Cc: connolly@w3.org, www-webont-wg@w3.org
Message-Id: <20020125074100K.pfps@research.bell-labs.com>
Summary:  I feel that I'm in a timewarp back to the '70s.  I sentence Jim
	  to go back and read all the ``What's in a ...'' papers and also
	  papers on first-order logic.

From: Jim Hendler <hendler@cs.umd.edu>
Subject: Re: CHAIR-NOTE: Defaults and etc.
Date: Fri, 25 Jan 2002 00:04:52 -0500

> >On Thu, 2002-01-24 at 21:06, Jim Hendler wrote:

> >[...]

> >>  for example:
> >>
> >>  :mammal a owl:class;
> >>      :birthmethod
> >>         [def:DefaultValue :LiveBear].
> >>
> >>  :platypus a :mammal;
> >>     :birthmethod :EggLaying.
> >>
> >>  :cow a :mammal;
> >>
> >>    That is what I do at the LANGUAGE level.
> >>
> >>  Now what does that mean?
> >>
> >>  This means any user who reads this is entitled to conclude all and
> >>  only those facts above and entailed by them.  This (according to D+O
> >>  semantics) means
> >>  it would be legitimate to conclude
> >>
> >>    :platypus :birthmethod :EggLaying.
> >
> >er... that much is stated in the input, yes, but...
> >
> >  >   :platypus :birthmethod [def:DefaultValue :LiveBear].
> 
> 
> You are right - I left out the statement that platypus was a subclass 
> of mammal, and that cow was a subclass of mammal - I should have made 
> this explicit:
> 
> :platypus a owl:class;
>    rdfs:subclass :mammal;
>    :birthmethod :Egglaying.
> 
> :cow a owl:class;
>    refs:subclass :mammal.

[...]

> and then, having made them explicit, it follows from
> the DAML+OIL axiomatic semantics which stated
> 
> 
> (<=> (PropertyValue subClassOf ?csub ?csuper)
>       (and (Type ?csub rdfs:Class)
>            (Type ?csuper rdfs:Class)
>            (forall (?x) (=> (Type ?x ?csub)
>                             (Type ?x ?csuper))))) [subClassOf axiom 2]

There is absolutely no reason that anyone should think that any properties
of objects except for some RDF(S) structural properties, such as rdfs:type,
can be deduced on subclasses of those objects.  This axiom certainly says
absolutely nothing about the inference of arbitrary properties on
subclasses, as can by easily determined by observing that there are no free
variables in the first position of PropertyValue predications.

There is no reason that any AI person should even be trying to make such
inferences go through without a ton of qualifications.  Properties of
classes, like cardinality, are very seldom also properties of their
subclasses, unless they are really characteristics of the members of the
class.  

Peter F. Patel-Schneider
Bell Labs Research
Received on Friday, 25 January 2002 07:41:17 GMT

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