A CLP Based Approach to HPSG

In this paper we present a CLP based method for the direct implementation of HPSG, a grammar formalism employing strongly typed feature structures and principles to constrain them. We interpret unification of typed feature structures under the restrictions of principled constraints as constraint solving in the CLP paradigm. The aim of our implementation method is to operationalize the declarative grammar specification without having to account for processing aspects, i.e. to clearly separate grammar and processing model. To achieve this goal we employ a lazy instantiation technique which maintains well-typedness of feature structures at every instantiation stage. This method is complemented with a delay mechanism enabling the constraints arising from grammar principles to cope with uninstantiated structures. Applicability conditions of grammar principles may be specified conditionally, viewing them as licensing conditions on every node of a feature structure. This also allows for the r..