[rules-users] not exists / forall(not) logically equivalent, behave differently

[Edson Tirelli]

    I believe there is an open ticket for a bug when using "not(exists())"
in 5.0. I did not investigated yet, but I believe this is a regression in
the new asymmetric matching algorithm in 5.0. Anyway, we will fix it before
releasing the final version.

    Meantime, just use:

not( Tail(dog == $dog) )

    Since the "exists" is redundant there because "not" is the existential
operator, not the "boolean" operator.

    []s
    Edson

2008/10/6 tim tim <timbaermannextra at googlemail.com>

> hello there,
>
> i have a rule, that should fire, when a required part of a whole is
> missing.
> lets say the whole is a dog, and the required part the tail.
> then the rule should fire, when there is a dog without a tail.
>
> i stated the rule in two logically equivalent ways.
>
> 1) when we have a dog, and all existing tails belong to other peoples dogs,
> the rule should fire:
>
> rule "no dog without a tail; forall"
>     when
>         $dog :Dog()
>         forall($t : Tail()
>                 Tail(dog != $dog))
>     then
>    // fire rule
> end
>
>
> 2) when we have a dog and no tail exists that belongs to this dog the rule
> should fire:
>
> rule "no dog without a tail; not exists"
>     when
>         $dog :Dog()
>         not( exists( Tail(dog == $dog)))
>     then
>    // fire rule
> end
>
>
> and they really do behave similar, but not the same..
> workingMemory.insert(dog);
> workingMemory.insert(dog.getTail());
> workingMemory.fireAllRules();
>
> // here both did not fire, but when i go on:
>
> workingMemory.modifyRetract(dogHandle)
> workingMemory.modifyInsert(dogHandle, dog)
> workingMemory.fireAllRules();
> // now the not(exists(..)) version did fire, whereas the forall(..) version
> did not.
>
>
> of course both rules should not have fired, nothing changed for the dogs
> relationship
> with its tail.
>
> i am using the 5.0.0.snapshot version of drools but i can not imagine that
> this is an
> unknown bug, as this is rather basic predicate logic.
> what am i missing?
>
> best, tim
>
>
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>


-- 
 Edson Tirelli
 JBoss Drools Core Development
 JBoss, a division of Red Hat @ www.jboss.com
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