[rules-users] Subclasses matche superclasses problem.

[nicolae oana]

Neil,

Thank you for your answer. 
You had right. My mistake was that I was calling modify(fact) each time 
after I set the theft assessment.

Best regards,
                     Oana      

Neil Goldman <ngoldman at teknowledge.com> wrote:     Oana,
   Although your example used a superclass/subclass  relationship, the problem is not due to that relationship,  You could just  as well have written two CAR rules :
   "if a car's price is <20000, then risk  of  theft is low"
  
   "if a car has the stealth radar avoidance option,  then risk of theft is high"
  
 You might be upset by the infinite loop, but there is no  way to know how you would like to assess the theft risk of a car that satisfies  BOTH conditions.
  
 Here are two ways you might deal with this.   
  
 a) maybe neither of  these conditions is really  sufficient to determine the theft risk, but simply to influence that risk.   The "then" part of the rule should just increment/decrement a value the  accumulates the net risk. But don't have the increment/decrement also tell  drools that the CAR was modified. 
  
 b) maybe the rules are TOTALLY ORDERED in your analytical  model, and the first rule that applies is the only one that matters.  You  can use SALIENCE in drools to capture ordering. If all the rules are in a single  activation group, then only the highest salience match will actually run (at  least, that is my understanding).  Again, you must not tell drools that the  CAR has been modified just because you set its theft  assessment.
  
  
  
  

  
---------------------------------
 From: rules-users-bounces at lists.jboss.org  [mailto:rules-users-bounces at lists.jboss.org] On Behalf Of nicolae  oana
Sent: Friday, February 16, 2007 2:11 AM
To:  rules-users at lists.jboss.org
Subject: [rules-users] Subclasses matche  superclasses problem.


 
Hi everybody,

I have a class Car which is superclass for class  ConvertibleCar, two rules (described below) and a ConvertibleCar fact in working  memory that causes both rules to fire, resulting this way an unwanted change to  the car`s attribute and an infinite loop. 

How do I evitate this problem:  the specialization class fact to not match its superclass column in a rule?  

ConvertibleCar car =new ConvertibleCar(10000);

rule  "rule-1"
    when 
        $car:Convertible()
    then
    $car.setPotentialTheftRating("high");
end

rule  "rule-2"
    when 
        $car:Car(price<20000)
    then
    $car.setPotentialTheftRating("low");
end

Best regards,  Oana


  

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