Category structures

  • Authors:

  • Gerald Gazda;Geoffrey K. Pullum;Robert Carpenter;Ewan Klein;Thomas E. Hukari;Robert D. Levine

  • Affiliations:

  • University of Sussex, Brighton, U.K.;University of California, Santa Cruz, Santa Cruz, California;University of Edinburgh, Edinburgh, U.K.;University of Edinburgh, Edinburgh, U.K.;University of Victoria, Victoria, B.C., Canada;University of British Columbia, Vancouver, B.C., Canada

  • Venue:
  • Computational Linguistics
  • Year:
  • 1988

Quantified Score

Hi-index 0.00

Visualization

Abstract

This paper outlines a simple and general notion of syntactic category on a metatheoretical level, independent of the notations and substantive claims of any particular grammatical framework. We define a class of formal objects called "category structures" where each such object provides a constructive definition for a space of syntactic categories. A unification operation and subsumption and identity relations are defined for arbitrary syntactic categories. In addition, a formal language for the statement of constraints on categories is provided. By combining a category structure with a set of constraints, we show that one can define the category systems of several well-known grammatical frameworks: phrase structure grammar, tagmemics, augmented phrase structure grammar, relational grammar, transformational grammar, generalized phrase structure grammar, systemic grammar, categorial grammar, and indexed grammar. The problem of checking a category for conformity to constraints is shown to be solvable in linear time. This work provides in effect a unitary class of data structures for the representation of syntactic categories in a range of diverse grammatical frameworks. Using such data structures should make it possible for various pseudo-issues in natural language processing research to be avoided. We conclude by examining the questions posed by set-valued features and sharing of values between distinct feature specifications, both of which fall outside the scope of the formal system developed in this paper.