A Problem-Solver/Tms Architecture for General Constraint Satisfaction Problems

Constraints, in various forms, are ubiquitous to design problems. In this paper, we provide a formalcharacterization of a generalized constraint satisfaction problem (CSP) that can be used to model manytypes of design/planning problems, and the architecture of an imlemented reasoning system for solving thisproblem. The architecture includes a truth maintenance system (TMS) which is specifically designed toreason about the relationships expressed in the constraints as a problem solution evolves. The CSPconsists of two types of data. The first type of datum corresponds to assignments that are handled by theproblem solver, and the second type corresponds to constraint terms handled by the TMS. Thedependency network, representing the relationships among constraint terms, is static and generally quitesmall, depending on the number of constraint terms. Also, justifications are never manipulated (onlyevaluated). This results in an architecture that makes efficient use of both space and time. The need forefficient TMSs, even though these might deal only with certain classes of problems, is underscored by thefact that general purpose TMSs have often been found to be highly inefficient for solving large problems.We also show how certain instances of the generalized CSP can be formulated as an integer programmingproblem, special cases of which can be solved efficiently using mathematical (integer) programmingtechniques.

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