Stable Solutions for Dynamic Constraint Satisfaction Problems

An important extension of constraint technology involves problems that undergo changes that may invalidate the current solution. Previous work on dynamic problems sought methods for eeciently nding new solutions. We take a more proactive approach, exploring methods for nding solutions more likely to remain valid after changes that temporarily alter the set of valid assignments (stable solutions). To this end, we examine strategies for tracking changes in a problem and incorporating this information to guide search to solutions that are more likely to be stable. In this work search is carried out with a min-connicts hill climbing procedure, and information about change is used to bias value selection, either by distorting the objective function or by imposing further criteria on selection. We study methods that track either value losses or constraint additions, and incorporate information about relative frequency of change into search. Our experiments show that these methods are generally eeective in nding stable solutions, and in some cases handle the tradeoo between solution stability and search eeciency quite well. In addition, we identify one condition in which these methods markedly reduce the eeort to nd a stable solution.