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Re: FOL versus Rule Languages - A tutorial

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Sat, 27 Aug 2005 00:47:16 -0400
To: Sandro Hawke <sandro@w3.org>
Cc: doug.foxvog@deri.org, Dieter Fensel <dieter.fensel@deri.org>, public-rule-workshop-discuss@w3.org, Christian de Sainte Marie <csma@ilog.fr>
Message-Id: <20050827044716.9C1A5CB5D3@kiferserv.kiferhome.com>

> > MMS is non-monotonic in that anything that cannot be proved
> > true in MMS is concluded to be false.  Adding any (non-provable)
> > ground statement or rule to a Herbrand model, limits the Herbrand
> > space and falsifies the conclusions that various statements are
> > false obtained from the earlier model.
> So MMS necessarily brings with it the CWA?
> I guess Flora-2 and Triple do this in a clever way, so they have MMS
> but their CWA is somehow scoped?

Actually, there is nothing really clever in what Flora-2 or Triple do. :-)
What they do is not a semantic trick, but a syntactic one.  They allow the
user to specify the scope of any inference (positive or negation)
explicitly, but the semantics remains like in traditional systems.
(Actually, Triple didn't have SNAF originally -- only positive scoped
inference. I am not sure if some later versions of Triple have default
negation, but this is not important here.)

I already hinted at how this is done when discussing Dan's example.
Basically, every rule-head (or fact) defined in a particular module is treated
as a predicate with a prefix that is specific to that module, and different
modules have different prefixes. In this way, if you ask a negated query 
against any predicate in a given module, then NAF and SNAF give the same
result because nothing outside of the module matters due to the uniqueness
of the predicate names that are local to that module.


>     -- sandro, wandering off to read more about Flore-2
Received on Saturday, 27 August 2005 04:47:27 UTC

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