Re: [rules-users] What's the difference between Drools and other constraints solvers?

Op 22-08-12 03:25, zjg_robin schreef: You only need those other object data structures if your constraints need them. They make your constraints readable and object orientated. Think about it, for example defining the dayOffRequest constraint: In Planner you base it on a DayOffRequest class and a ShiftAssignment class, by using DayOffRequest.getEmployee() and DayOffRequest.getShiftDate(). In LP based solvers, there is no DayOffRequest class and a ShiftAssignment class, instead they are represented as ints, int arrays or even arrays of arrays of ints. No code encapsulation, no OO. In fact, you have to manually translate id's into indexes (because id's have gaps and indexes can't have gaps). For example, in Planner you write it like this. Notice that you can read it. // Requested day on/off rule "dayOffRequest" when $dayOffRequest : DayOffRequest($e : employee, $d : shiftDate) $assignment : ShiftAssignment(employee == $e, shiftDate == $d) then ... // dayOffPenalty = $dayOffRequest.getWeight() end Notice how $dayOffRequest and $assignment are typed variables. In LP you have to write: dayOffPenalty <- sum[dayOffRequestArray in dayOffRequestArrays](shiftAssignmentArray[employeeIndexFromId[dayOffRequestArray[0]]][dayOffRequestArray[1]] * dayOffRequestArray[2]); Notice how the "dayOffRequestArray[2]" magically means it's the weight. What do "dayOffRequestArray[1]" and "dayOffRequestArray[0]" mean? What if the weight is a BigDecimal instead of an int? And despite lacking that mathematical equation, Planner has better results (as shown in the competitions :)