Thanks Geoffrey,

I really like you're suggestion to use intermediate facts to keep the employee's seniority. After this email, I will try to implement it, but I do have a question about your way to implement it. Since my goal is to make senior employee ($higherRankedEmployee) work before a less senior employee ($lowerRankedEmployee), I think the rule should contain a 'not' or a 'not exists' expression. It may be stated as follow : 

rule "hard-Seniority"
when
         EmployeeRanking($higherRankedEmployee, $lowerRankedEmployee, $numberOfEmployeesInRankBetweenThem)
         PlanifEventAssignment(employee == $lowerRankedEmployee)
         not PlanifEventAssignment(employee == $higherRankedEmployee)
then
  insertLogical(new IntConstraintOccurrence("hard-Seniority",
         ConstraintType.NEGATIVE_HARD,
          $numberOfEmployeesInRankBetweenThem,
         $employee, $assignment));
end

Thanks

2011/12/8 Geoffrey De Smet <ge0ffrey.spam@gmail.com>


Op 07-12-11 21:41, Patrik Dufresne schreef:
Hi all,

I'm trying to create rules to model my problem. So far, I didn't manage to create rules to make Drools converge to a solution because of score traps. I don't see any way to avoid it (as I'm not an expert with Drools). I can express the rule as follow : a senior employee should work before a less senior employee.

I've implement it as a hard constraint :
rule "hard-Seniority"
when
$employee : Employee()
$assignment : PlanifEventAssignment( $planifEmployee : employee )
What's does this $planifEmployee do?

not PlanifEventAssignment( employee == $employee )
eval(Helper.compareEmployee($employee, $planifEmployee) < 0)
then
insertLogical(new IntConstraintOccurrence("hard-Seniority",
        ConstraintType.NEGATIVE_HARD,
         1,
         $employee, $assignment));
end

The function Helper.compareEmployee(e1, e2) return -1 if e1 is more senior then e2 (mostly based on hire date and other boolean fields).

On first sight, in Solution.getProblemFact() I would add these cached problem facts, for any 2 employees (but just once per combination):
new EmployeeRanking(higherRankedEmployee, lowerRankedEmployee, numberOfEmployeesInRankBetweenThem)

then you can do
 
rule "hard-Seniority"
when
         EmployeeRanking($higherRankedEmployee, $lowerRankedEmployee, $numberOfEmployeesInRankBetweenThem)
         PlanifEventAssignment(employee == $lowerRankedEmployee)
         PlanifEventAssignment(employee == $higherRankedEmployee)

then
insertLogical(new IntConstraintOccurrence("hard-Seniority",
        ConstraintType.NEGATIVE_HARD,
         $numberOfEmployeesInRankBetweenThem,
         $employee, $assignment));
             


This way, the rule make sure a senior employee is working. But it's a score trap since, many moves are required to resolve the constraint. e.g:

PlanifEventAssignment1 = e2
PlanifEventAssignment2 = e3
PlanifEventAssignment3 = e4
PlanifEventAssignment4 = e5

e1 is not working. Multiple move are require to reach the best solution : 
PlanifEventAssignment1 = e1
PlanifEventAssignment2 = e2
PlanifEventAssignment3 = e3
PlanifEventAssignment4 = e4

So I'm asking you. What is the best way to make Drools converge ? Do I need to change my rule, or should I create a BigMove ?
course grained moves will work mostly, but solving the score trap itself is a far better long-term solution (and it still allows you to add course grained moves later).

--
Patrik Dufresne

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-- 
With kind regards,
Geoffrey De Smet

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--
Patrik Dufresne