A logic-based grammar formalism incorporating feature-structures and inheritance

Abstract

The use of Definite Clause Grammars (DCGs) to describe Natural Language grammars as logic programs has been particularly fruitful in building NL interfaces for relational databases. First-order logic, however, suffers from several shortcomings as a language for knowledge representation and computational linguistics. This dissertation describes a new logic, called $\psi$-logic, remedying these shortcomings. NL processing is one application of $\psi$-logic and the Inheritance Grammar formalism, whose semantics are rooted in $\psi$-logic, is also defined. First-order logic is a special case of $\psi$-logic and, consequently, every DCG is an Inheritance Grammar. This logic differs from traditional logic in that the primary data structure encompasses the feature-based structures used in unification-based grammatical formalisms such as PATR. In addition, an ordering on the symbols of the grammar facilitates taxonomic reasoning, a problematic task in DCGs. An interpreter for $\psi$-logic programs has been implemented (in Smalltalk) and various implementation techniques have been explored. In addition, several Inheritance Grammars have been implemented and the perspicuity of the Inheritance Grammar formalism is discussed.