A CLP Schema to Integrate Specialized Solvers and its Application to Natural Language Processing

The problem of combining different constraint solvers has been mentioned among others by [25], [13], [17], [20] without giving satisfactory solutions. We propose a general framework for implementing specialized reasoners/constraint solvers in a logic programming environment using semantic unification. It allows for a modular and declarative definition of the interactions of such reasoners. This is achieved by by using attributed variables [15] as a data-structure relating a variable to the set of all constraints for this variable. Conditional rewrite rules specify simplification and possible interactions of these constraints. A few examples will demonstrate constraints relating to single variables and interactions thereof. We will demonstrate, how this framework leads to a very natural and concise formulation of principles, grammar and lexicon in a hpsg like formalism. Furthermore the necessity of extending the framework to handle constraints relating two or more variables will be dis..