Computing Explanations for Global Scheduling Constraints

Integration of explanations into a CSP solver is a technique addressing difficult question “why my problem has no solution”. Besides providing some sort of answer to the user, explanations can be used for debugging, solving dynamic problems, and advanced search algorithms. Explanations work pretty well with simple constraints. However, in order to use explanations together with a global constraint, its filtering algorithm (i.e. propagation) has to be enhanced to be explanation-aware. This paper proposes such a technique, suitable for some sort of propagation algorithms (e.g. some versions of edge-finding and not-first/notlast). For edge-finding algorithm, this technique is then further improved.