CP 04 Tutorial : Distributed Constraints Satisfaction Algorithms , Performance , Communication ?

Distributed constraints satisfaction problems (DisCSPs) have been studied for over a decade. The first distributed search algorithm was asynchronous backtracking, which is still the most studied. In the last few years, several new families of distributed search algorithms have been investigated and comparative experimental studies are encouraging. A natural extension to distributed constraints satisfaction is distributed constraints optimization. Stochastic search algorithms for solving DisCSPs, such as Distributed Breakout, have appeared a few years ago. Distributed stochastic search algorithms are naturally suitable for solving distributed optimization. In contrast, asynchronous search algorithms for distributed optimization have been proposed in recent years. Due to the distributed nature of the problem, message delay can have unexpected effects on the behavior of algorithms on DisCSPs. This has been shown in an experimental study that induced random delays on messages sent among agents. In order to study the impact of message delays on DisCSP search, a model of delays in terms of concurrent performance measures is needed. Within such a model, the behavior of families of search algorithms in the presence of delays is varied and interesting. An important feature of the distribution of the problem among agents is their ability to maintain some privacy. Agents may not want to share their values with other agents, and they may wish to keep constraints as private as possible. Some recent work has resulted in versions of asynchronous backtracking that maintain both privacy of values and privacy of constraints. Other investigations of privacy in DisCSPs focused on the analysis of information gain by studying a welldefined problem, that of scheduling meetings of agents.