A Rule-based Approach to Dynamic Constraint Satisfaction Problems

Dynamic Constraint Satisfaction Problems Armin Wolf GMD { German National Research Center for Information Technology GMD FIRST, Kekul estra e 7, D-12489 Berlin, Germany E-mail: [email protected] URL: http://www.first.gmd.de Abstract Practical constraint satisfaction problems (CSPs) are rarely statically xed. For instance, in job-shopscheduling express jobs have to be added, while already planned jobs are canceled. In this dynamic environments previously occupied resources like machines and sta members have to be set free for further usage. In established Constraint Programming systems the dynamics of CSPs are not well supported. In fact, all state-of-the-art systems support incremental additions of constraints but deletions are in general supported via chronological backtracking. This results in a loss of performance in dynamic environments with continuous changes of the CSPs to be solved. For nite domain constraint problems, several approaches exists overcoming this drawback while supporting arbitrary additions and deletions of constraints. However, these approaches are domain-speci c, a generalpurpose approach for solving DCSPs is still missing. In fact, there are Constraint Handling Rules (CHRs) successfully used to solve several CSPs but only constraint addition and chronological backtracking is supported. Based on CHRs a new rule-based method for solving Dynamic CSPs (DCSPs) is presented supporting arbitrary constraint additions and deletions.