# Re: [PRD] Rule instances, refraction and Modify [Was: Re: Fwd: Clips behavior]

From: Gary Hallmark <gary.hallmark@oracle.com>
Date: Tue, 02 Feb 2010 08:27:26 -0800
Message-ID: <4B68526E.20509@oracle.com>
To: Christian De Sainte Marie <csma@fr.ibm.com>

```

Christian De Sainte Marie wrote:
>
> All,
>
> Gary wrote on 01/02/2010 01:01:11:
> >
> >> 3. the binding of the rule (universal) variables is not always
> >> discriminant enough to characterize a rule instance [...]
> >
> > Can you do a simple transformation:
> >
> > Rule: FORALL ?x, ?y, ?z, IF test(?x) AND ( ?y=1 AND foo(?y) OR ?
> > z=B AND bar(?z) ) THEN...
> >
> > And then use our existing rule instances. I'm a bit concerned about a
> > new notion of matchedFact. I don't know what that is, exactly.
>
> As we discussed yesterday, this would be a very nice way to correct
> the problem and cover the case of disjunctive rules.
>
> Unfortunately, I cannot find the right way to normalize :-(
>
> The transformation that you propose does not work, since ?y will
> always be bound to 1 and ?z to B, whether the instance matched foo(1)
> or bar(B) (and, thus, the two different instances will always have the
> same bindings for all their universal variables).
I don't understand. Surely if the only fact is foo(1), then ?y is bound
to 1 and ?z is unbound. Similarly, if the only fact is bar(B), then ?y
is unbound and ?z is bound to B...
>
> I could not find a way to keep the current definition of rule instance
> and still cover the case of disjunctions without adding a dummy
> variable that differentiate the disjuncts. Something like:
>
> Rule: FORALL ?x ?y, IF test(?x) AND ( (foo(1) AND ?y=1) OR (bar(B) AND
> ?y=2) ) THEN...
>
> That's ugly, but that works. So, the trick is not to normalize the
> conditions in a way similar to CLP for the purpose of defining rule
> instances, but define rule instances wrt to rules are put in the same
> disjunctive normal form as specified for the purpose of defining
> safeness, with an extra universal variable added, that is equated to a
> different value in each top-level disjunct.
>
> Since we can reuse the same normal form as for defining safeness, the
> change in hte text is not that big (something like a couple lines
> added before the -essentially unchanged- definition of rule instance).
>
> That solution is less elegant than what Gary suggested, but I cannot
> find a better one; and it works (since it is essentially equivalent to
> rewriting disjunctive rules into a set of conjunctive ones).
>
> I propose that we use it, unless or until somebody finds a better way
> to do the same thing.
>
> Cheers,
>
> Christian
>
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```
Received on Tuesday, 2 February 2010 16:28:10 UTC

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