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>

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 http://www.informatik.tu-cottbus.de/~gwagner Email: G.Wagner@tu-cottbus.de Brandenburg University of Technology at Cottbus, GermanyReceived on Wednesday, 29 June 2005 10:25:22 UTC

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