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RE: here's a draft charter strawman slideset, wrt W3C Rules WG

From: Gerd Wagner <wagnerg@tu-cottbus.de>
Date: Wed, 29 Jun 2005 12:22:54 +0200
To: "'Jos de Bruijn'" <jos.debruijn@deri.org>, "'Francois Bry'" <bry@ifi.lmu.de>
Cc: <public-rule-workshop-discuss@w3.org>
Message-Id: <20050629102344.1DA86508219@smtp2.TU-Cottbus.De>

> > 2.1 views, or predefined queries (rfegardless of whether they are
> > evaluated by forward of bac kwartd chaining, I fully agree with the
> > proposal in this respect).
> >
> > 2.2 Integrity constraint-like rules, i.e. FOL-like or Description
> > Logic-like, eg OWL, formuylas evaluated against a repository of
> > factual data (eg database).
> >
> > 2.3. Ontology-like rules, i.e. FOL- or Description LOic-likre, eg
> > OWL formulas considered independently of any repository of factual
> > data.
> I would say 2.3 incorporates both 2.1 and 2.2. OWL incorporates both
> derivation rules (e.g. subclass axioms) and integrity rules (e..g.
> disjointness axioms).

The same could be said about SWRL. But the real problem is that
they are all just axioms in the sense of ("good old-fashioned"?) 
mathematical logic. So, in fact, OWL does not support the 
computational logic distinction between definitions (derivation 
rules) and constraints (integrity rules). That's why people, when 
they want to define a class and then specify a constraint for it, 
using OWL and SWRL, may be puzzled by the logical consequences:
the don't get what they intended to get!
> There has already been a lot of discussion on how to integrate OWL and
> rules. The two leading (well-known) ways to integrate them are:
> - - use of a common subset; disadvantage is that many (especially DL
> advocates) believe that this subset is too small for any 
> useful ontology
> - - exchange of consequences between the OWL KB and the rule 
> base (e.g. dl-programs by Eiter et al.)

There is a natural third option: evolve OWL and its mathematical
logic semantics into a more natural Web vocabulaly specification
language OWL2, designed to work in conjunction with rules (which 
OWL1 was not), and based on a computational logic semantics.

> It would, IMHO, be interested to see how we could relate OWL
> (open-world) constraints, which are very helpful when reasoning 
> over the schema, and closed-world (and UNA) integrity constraints 
> which can be used to check a set of data. 

We can perform both open-world and closed-world reasoning using
a language with two kinds of negation (such as RuleML or the one
developed by the REWERSE working group I1, which is called "R2ML",
standing for "REWERSE Rule Markup Language") whose semantics is 
based on partial logic. So we just have to evolve OWL and its 
current limited semantics towards partial logic (and some concept 
of intended/preferred model).

Gerd Wagner 
Email: G.Wagner@tu-cottbus.de
Brandenburg University of Technology 
at Cottbus, Germany
Received on Wednesday, 29 June 2005 10:25:22 UTC

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