[rules-users] Hard constraints to enforce employee seniority

[Geoffrey De Smet]

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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