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Re: A Rough Guide to Notation3

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Sat, 24 Aug 2002 18:18:00 -0400 (EDT)
Message-Id: <20020824.181800.34998459.pfps@research.bell-labs.com>
To: sandro@w3.org
Cc: seth@robustai.net, sean@mysterylights.com, www-rdf-interest@w3.org

From: Sandro Hawke <sandro@w3.org>
Subject: Re: A Rough Guide to Notation3 
Date: Sat, 24 Aug 2002 17:52:12 -0400

[Lots of tangential stuff about inconsitencies and information removed.]

> > The problem is not their (potential) existence.  It is their existence
> > everywhere.  The problem is that if you allow self-referential
> > sentences and also need to have sentences exists everywhere, removing just
> > the problematic ones is problematic. 
> 
> I don't quite follow that, sorry.

The problem with some self-referential sentences, such as the self negating
one, is that they have no models, not even models that assign them a truth
value of false.  

This is not a problem for a DAML+OIL.  Entailment defined on top of
DAML+OIL would be very weak, because not all DAML+OIL classes need exist in
all DAML+OIL interpretations.  Mentioning the analogue of a self-negating
sentence in DAML+OIL is like stating a contradiction.

However, if DAML+OIL is to be given a reasonable notion of entailment, so
that, for example, John in Student and John in Employee entails John in the
intersection of Student and Employee, then all DAML+OIL classes must
exist in all DAML+OIL interpretations.  However, this then includes the
problematic ones, which ends up with all DAML+OIL knowledge bases having no
interpretations.

Trying to forbid just the problematic classes requires something like ``A
class is acceptable syntactially if it is acceptable semantically'' which
is itself problematic.

>    -- sandro

Again, there are lots of ways around this problem, just none that fit into
the strong version of the RDF philosophy.

peter
Received on Saturday, 24 August 2002 18:18:11 GMT

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