The difference is actually that the not in Rule1 doesn't have a
preceding pattern, and therefore Jess inserts (initial-fact), so that
the rule won't work unless you've executed (reset) at the beginning of
the session, as described in section 6.10 of the Jess 7.1 manual. See
http://www.jessrules.com/jess/docs/71/rules.html#not_ce
On 1/6/12 8:40 AM, Theodore Patkos pat...@ics.forth.gr wrote:
Hello everyone and best wishes for the new year
could someone please give me an explanation why the following two rules
behave in a different way, although they express the same logical
formula (i.e., not (Object ^ Pred) )? In fact, only the second rule
reaches correct conclusions, as I note below.
(defrule Rule1
(not
(and
?o - (Object (name B))
(Pred (obj ?o))
))
=
(printout t OK1 crlf)
)
(defrule Rule2
(or
(not (Object (name B)))
(and
?o - (Object (name B))
(not (Pred (obj ?o)))
))
=
(printout t OK2 crlf)
)
The definition of facts could be like:
(deftemplate Object (slot name))
(assert (Object (name A)))
(assert (Object (name B)))
(deftemplate Pred (slot obj))
where obj is the id of some Object fact, eg.
(defrule Rule
(declare (salience 10))
?o - (Object (name A))
=
(assert (Pred (obj ?o)))
)
What I notice is that Rule1 behaves erroneously when the Object fact
exists in the KB, but not the Pred fact: although it is supposed to be
triggered, it is not! Rule2, on the other hand, behaves correctly all
the times.
When both Object and Pred facts exist or when the Object does not exist,
both rules behave fine.
So, what is wrong with the syntax of the first rule? No variable
definition is used outside the not pattern..
Thanks
Theodore
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