Hierarchical Constraint Logic Programming Languages

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Constraint Logic Programming (CLP) is a general scheme for extending logic programming languages to include constraints. However, CLP languages, as well as most other constraint-based languages and systems, only allow the programmer to specify constraints that must hold. In many applications, such as interactive graphics, page layout, and decision support, one needs to express preferences as well as strict requirements. The authors have designed a generalization of the CLP scheme, Hierarchical Constraint Logic Programming (HCLP), which allows a programmer to express both required and preferential constraints, with an arbitrary number of strengths of preference. Development of HCLP will continue on the practical side, a goal is to improve the implementation of an instance of the language scheme, including incorporating efficient constraint solvers and adding new ways of comparing potential solutions. Its utility will be tested by using interactive graphics, as well as document formatting, decision support, and scheduling, as test applications. On the theoretical side, it is planned to extend the constraint hierarchy formalism to include read-only variables and partially ordered hierarchies.