Constraint Based System(CBS) : Example
For the CBSs, all the variables should be defined at product model definition time. If we want to add, delete, or modify the constraints, the system should be remodeled. Therefore it is inappropriate for incremental revision support under dynamic constraints and preferences.
Did you check the short description of "Secretaries' Nightmare"? If not, click here.
Did you check the functional block diagram for constraint based systems? If not, click here.
*For simplicity, only the first meeting constraint will be considered
- Given constraints and preference definitions, the system will perform constraint propagation and the result is consistent sets as { 7, 8, 25 }
- Following the preferences, the system will decide values as [MD1,7], [Axel1,7], [Dirk1,8]. This is constraint violated. Records current decisions for backtracking(red characters).
- Another decision will be made as [MD1,7], [Axel1,7], [Dirk1,7],[Brigitt1,8]. This is constraint violated. Records current decisions for backtracking(blue characters)
- Find solution as [MD1,7], [Axel1,7], [Dirk1, 7]and [Brigitt1, 7].
But what will happen if one constraint is deleted? Assume Brigitt needs not attend the meeting.
Input is changed. Constraint propagation should be performed again(see the consistent sets { 5,7,8,25}). "Decision maker" and " consistency check" should be remodeled. Backtracking records are useless. Eventually the system should be remodeled. In case of a preference change, "Decision maker" should be remodeled and the system will try to solve the problem from the scratch because we can not guarantee that the current solution is the best. In any case, the system is very inefficient because incremental change can not be controlled and the problem solving history is lost.
Heecheol Jeon : jhc@cdr.stanford.edu