Implementing Constraint Solvers: Theory and Practice

Our research is based on Constraint Handling Rules (CHR), a powerful language for writing constraint solvers. We investigate confluence of CHR programs. This property guarantees that a CHR program will always compute the same result for a given set of constraints independent of which rules are applied. We give a decidable, sufficient and necessary syntactic condition for confluence. Finally we present an application utilizing CHR offering rent advice: The city government of Munich regularly publishes a booklet called the "Mietspiegel " (MS). The MS basically contains a verbal description of an expert system. It allows to calculate the estimated fair rent of a flat. With our computerized version, "The Munich Rent Advisor", we extended the functionality and applicability of the MS so that the user need not answer all questions of the form. The key to computing with partial information was to use constraint technology. 1 Introduction Logic Programming (LP) originates from the discovery t..