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Re: Action-67 some examples on b-nodes issues and their impact on users

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Wed, 23 Jan 2008 03:13:57 -0500 (EST)
Message-Id: <20080123.031357.65552764.pfps@research.bell-labs.com>
To: jpan@csd.abdn.ac.uk
Cc: public-owl-wg@w3.org

From: "Jeff Z. Pan" <jpan@csd.abdn.ac.uk>
Subject: Action-67 some examples on b-nodes issues and their impact on users
Date: Tue, 22 Jan 2008 22:53:07 -0000 (GMT)

> >Action 67: Jeff to lead effort on formulating some examples on
> b-nodes issues and their impact on users
> As Boris pointed out in the telecon, there was already a nice
> example (hidden behind some rather technical discussions) in his
> earlier email:
> http://lists.w3.org/Archives/Public/public-owl-wg/2007Nov/0177.html
> In short, there are two choices for semantics of anonymous
> individuals (b-nodes):
> 1) existentially quantified variables
> 2) skolem constants
> Example:
> Given an ontology O about friends (suppose there are no anonymous
> individuals in O). Let us consider the following extra individual
> axioms (where :_1 is an anonymous individual):
> hasFriend(Bob,:_1)
> hasAge(:_1,"26"^^xsd:integer)
> With both semantics, the axioms both roughly say "Bob has some
> friend aged 26" with some subtle difference: under semantics 1),
> the friend aged 26 could be someone already mentioned in O, while
> under semantics 2), the friend is someone new and cannot be
> someone mentioned in O.

I do not believe that this is an accurate English gloss of the actual
formal situation.

[I'm going to use an FOL syntax below to emphasize the difference
between the two situation.]

If we have a KB that does not mention some constant, say fB, then the
difference between 
	Ex hasFriend(Bob,x) & hasAge(x,26)
	hasFriend(Bob,fB) & hasAge(fB,26)
is not that fB is or is not equal to any other constant in the KB.

With only the above information, there would be interpretations in which
the denotation of x is the same as the denotation of some (other)
constant and interpretations where the denotation of x is different from
that of all (other) constants and similarly for fB.

> (The above is true unless we have some further extra axioms
> forcing :_1 to be the same as some known individuals.)

> Comments/Further examples are welcome.
> Jeff

Received on Wednesday, 23 January 2008 08:43:05 UTC

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