If I understand the previous posts correctly, backward-
chaining was achieved in Jess using forward-chaining and
so one is really just the "opposite" of the other?
Can any problem be solved with relative ease using either
forward or backward chaining or is it the case that certain
problems lend themselves to a particular approach?
It has seemed to me that modelling database access is easiest
achieved using backward-chaining.
Would it be possible to use forward-chaining to perform
database queries? Would it be natural?
Does it really depend on how you state the problem to
be solved or are there determining factors that lead
one to use a method over another?
Thanks
John.
----Original Message Follows----
In Jess, the pattern (not (q)) means there is no fact (q).
In Jess's backward chaining, you write a special kind of rule that can
generate (q), and it is triggered when a (q) fact would be matched but
there isn't one -- i.e., when (not (q)) is true. The other premises of
this special rule would collectively be 'p' in your example.
So if something is interested in (q), but there is no (q), the special
rule is triggered -- but it will only fire if (p) is true. Therefore
in a real sense, (p) implies (q), and (not (q)) implies (not (p)) --
i.e., if (q) can't be created, it is because (not (p)).
So I think what Jess does matches your textbook description rather
well, given the forward-chaining framework in which it works.
I think Patrick Tang wrote:
> Hi,
>
> I want to ask a general question on backward chaining in rule system,
>
> I have found some books on logic and they have definition on backward
> chaining as follows,
>
> given a rule, p implies q,
> then by backward chaining, it need to start with (negation q), to
> imply (negation p),
> i.e. ~q implies ~p, that is their definition on backward chaining.
>
> But in many rule systems Jess, they perform backward chaining without
> any negation,
> why are the differences ?
>
> Thanks
>
> Patrick
>
---------------------------------------------------------
Ernest Friedman-Hill
Distributed Systems Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
Org. 8920, MS 9012 [EMAIL PROTECTED]
PO Box 969 http://herzberg.ca.sandia.gov
Livermore, CA 94550
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