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OFAI-TR-92-37 ( 48kB g-zipped PostScript file)

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

Bernhard Pfahringer, Johannes Matiasek

The problem of combining different constraint solvers has been mentioned among others by (Schroedl 1991, Holzbaur 1990, Lim and Stuckey 1990, Nelson and Oppen 1980) 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 using `attributed variables' (Huitouze 1990) 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 discussed.

Keywords: , Constraints, Logic Programming, HPSG

Citation: Pfahringer B., Matiasek J.: A CLP Schema to Integrate Specialized Solvers and its Application to Natural Language Processing, Austrian Research Institute for Artificial Intelligence, Vienna, TR-92-37, 1992.