Coordination in Unification-Based Grammars

Abstract

Within unification-based grammar formalisms, providing a treatment of cross-categorial coordination is problematic, and most current solutions either over-generate or under-generate. In this paper we consider an approach to coordination involving "composite" feature structures, which describe coordinate phrases, and present the augmentation to the logic of feature structures required to admit such feature structures. This augmentation involves the addition of two connectives, composite conjunction and composite disjunction, which interact to allow crosscategorial coordination data to be captured exactly. The connectives are initially considered to function only in the domain of atomic values, before their domain of application is extended to cover complex feature structures. Satisfiability conditions for the connectives in terms of deterministic finite state automata are given, both for the atomic case and for the more complex case. Finally, the Prolog implementation of the connectives is discussed, and it is illustrated how, in the atomic case, and with the use of the freeze/2 predicate of second generation Prologs, the connectives may be implemented.