From: Gerd Wagner <wagnerg@tu-cottbus.de>

Date: Fri, 26 Aug 2005 11:33:50 +0200

To: "'Dieter Fensel'" <dieter.fensel@deri.org>, <public-rule-workshop-discuss@w3.org>

Cc: "'Christian de Sainte Marie'" <csma@ilog.fr>

Message-Id: <20050826093514.6937450821F@smtp2.TU-Cottbus.De>

Date: Fri, 26 Aug 2005 11:33:50 +0200

To: "'Dieter Fensel'" <dieter.fensel@deri.org>, <public-rule-workshop-discuss@w3.org>

Cc: "'Christian de Sainte Marie'" <csma@ilog.fr>

Message-Id: <20050826093514.6937450821F@smtp2.TU-Cottbus.De>

Just some supplementary explanations to Dieter's "tutorial": > But the essence stays the same. The semantics is truly > defined declarative in terms of a defined model and not > in terms of an evaluation strategy of rules. As you said before, it's not necessarily defined in terms of a (i.e. exactly one) preferred/intended model but may be defined in terms of a set of preferred/intended models. > And that extension are truly monotonic in the sense that in > the case of a restricted sublanguage the confirm with the simpler > definition of the unique model. Such an extension of a formalism is normally called "conservative", not "monotonic". > 3.1) In rule languages we restrict ourselves to a certain type > of interpretations/models which are called Herbrand models. Yes, but in general we may relax this and allow (suitably defined) Herbrand-like models (e.g. for accommodating non-unique names). > 3.2) NOW COMES the important difference. In FOL we reason > about ALL Herbrand models. Not just about Herbrand models but about all kinds of models. That means even very strange/unintended models are taken into account. > With rule languages we select a certain Herbrand > model as the ground of our inference. As already said above, we do not necessarily select just one, but possibly several, intended models. > "Assume you have > > p(a,b), p(b,c) > and the following two rules: > p(x,y) -> q(x,y) > p(x,y) & p(y,z) -> q(x,z) > > Then under minimal model semantics q is the deductive closure I think this is normally called "transitive closure". > of p, i.e., q(a,b), q(b,c), q(a,c) are true and no other q(x,y) > is true. So, this example shows nicely the superiority of the intended model semantics approach for computational specification languages. -Gerd --------------------------------------------- LS Internet-Technologie http://www.informatik.tu-cottbus.de/~wwwitec/ Tel: 0355-69-2397 Email: G.Wagner@tu-cottbus.deReceived on Friday, 26 August 2005 09:35:26 GMT

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