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Re: On production rules and phase I&II

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Wed, 08 Mar 2006 01:53:46 -0500
To: Frank McCabe <frank.mccabe@us.fujitsu.com>
Cc: public-rif-wg@w3.org
Message-ID: <9038.1141800826@kiferserv.kiferhome.com>


> 
> The lack of recursion comes from the mapping into
> isTrue(C) <- A ^ B
> 
> Actually, the mapping I saw for phase I PRs was
> 
> mustBeTrue(C) <- A ^ B

Where did you see this mapping. It is definitely not an agreed upon
mapping.


> which is a closer fit to the original meaning of assert; since C *may  
> not* be true prior to the use of the rule.
> 
> To support chaining in PRs you must go on from mustBeTrue to being  
> true! That is where possible worlds comes in -- if you want to be  
> halfway faithful to the intent of PRs.
> 
> Also, I understand that chaining in PRs is not  necessarily automatic  
> (what is?) Hence you may wish to suppress chaining. Hence the lack of  
> recursion.

If suppression of chaining is going to get into RIF at all, it won't be
part of Phase I and will require additional syntax that would take it out
of Horn.


	--michael  


> I apologize if I gave the impression that the logic part of Phase I  
> would not support recursion, I would have been flabbergasted to hear  
> that!
> 
> Frank
> 
> On Mar 7, 2006, at 3:10 PM, Peter F. Patel-Schneider wrote:
> 
> > From: Frank McCabe <frank.mccabe@us.fujitsu.com>
> > Subject: On production rules and phase I&II
> > Date: Tue, 7 Mar 2006 14:56:37 -0800
> >
> >>
> >> Part of the proposed plan is to partition the handling of production
> >> rules across the phases, with phase I being the 'pure' subset of
> >> production rules.
> >>
> >> The pure subset corresponding to an extremely small subset of horn
> >> clause logic (no recursion!) and an extremely small subset of PR (no
> >> modify or remove in the action part of the rule)
> >
> > I don't understand where the "no recursion" comes from here.  Could  
> > you perhaps
> > point to evidence that recursion is not going to be part of phase I?
> >
> >> Quite apart from the fact that that to isolate this small subset of
> >> PRs is to completely miss the point & approach of PRs, there is a
> >> further technical issue.
> >>
> >> It is possible to map a rule of the form
> >>
> >> when A & B then assert C
> >>
> >> into a 'horn clause' of the form
> >>
> >> isTrue(C) <- A ^ B
> >
> > Well, maybe, but wouldn't it be much better to just map it into
> >
> > 	C <- A ^ B
> >
> >> A point to bear in mind: to support chaining, it will be nec. to
> >> conclude from
> >>
> >> isTrue(C)
> >>
> >> to
> >>
> >> C
> >>
> >> This appears to imply a Kripke-style possible world semantics.
> >
> > Why?  Even if one was to utilize isTrue, then why would isTrue just  
> > be a truth
> > predicate, which does not require a Kripke-style semantics.
> >
> > [ Some interesting issues having to do with retraction removed. ]
> >
> >> Frank
> >
> > Peter F. Patel-Schneider
> 
> 
> 
Received on Wednesday, 8 March 2006 07:17:13 GMT

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