[rules-users] how "exists" works exactly?

[fgadrat at genigraph.fr]

Hi Antonio,
Documentation states that the complement to "not" is "exists",whereas "not" keyword is used to match the absence of a fact (in Working Memory), and "exists" keyword is used to test the existence of one or more facts (in Working memory).

So if you want to test that a fact is not in working memory, then you should  use the 
not(MyClass()) pattern.

Hope this helps,
Francois.

Antonio Neto <antoniosouzaneto at gmail.com> a écrit :

> Any idea? Please...
>
> 2010/5/4 Antonio Neto <antoniosouzaneto at gmail.com>
>
>> Hi all,
>>
>> I don't know exactly why I have a problem in my "exists" function. I've
>> tried many different ways, but it does not work. Anybody could help me,
>> please?
>>
>>
>> I have the following rules:
>>
>> *rule "diff"
>> when
>>     $var1: EReference(name == "employee")
>>     $var2: EClass(name == "Company", EAllReferences contains $var1)
>>     not (exists( EPackage(EClassifiers contains $var2 ) ))
>> then
>>     insertLogical(new IntConstraintOccurrence("diff", 10));
>> end
>>
>> rule "ClassesNotReferenced"
>>     when
>>         $q1 : EClass();
>>         $q2 : EPackage(EClassifiers contains $q1);
>>         not( exists ( EReference(EType == $q1) ));
>>     then
>>         insertLogical(new IntConstraintOccurrence("ClassesNotReferenced",
>> 1, $q1));
>> end*
>>
>>
>> and in my facts (and my EPackage) I have 4 instances of EClass "Company"
>> with a EReference "employee", and another EClass "Person".  I still have a
>> "move" that removes EClasses in my Drools Solver.
>>
>> I need to have only one classe "Company" after processing. But it removes
>> only the EClass "Person", when it was supposed to remove one EClass "Person"
>> and 3 ECLasses "Company". Leaving one EClass "Company" in the end.
>>
>> The problem is:  when Drools tries to remove a EClass "Person" it thinks
>> that  the EClass "Company" does not exists. But in fact there are 3 others.
>>
>> Any clue about it, please ?
>>
>> Thanks
>>
>> Bests regards
>>
>> Antonio
>>
>>
>>
>
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