Constraints on the Generation of Adjunct Clauses

CONSTRAINTS ON THE GENERATION OF ADJUNCT CLAUSES Alison K. Huettner* Marie M. Vaughan ** David D. McDonald ** Department of Linguistics * Department of Computer & Information Science ** University of Massacusettts Amherst, Massachusetts 01003 ABSTRACT This paper presents an analysis of a family of particular English constructions, all of which roughly express "purpose". In particular we look at the purpose clause, rationale .clause, and infinitival relative clause. We (1) show that couching the analysis in a computational framework, specifically generation, provides a more satisfying account than analyses based strictly on descriptive linguistics, (2) describe an implementation of our analysis in the natural language generation system MUMBLE-86, and (3) discuss how our architecture improves upon the techniques used by other generation systems for handling these and other adjunct constructions. 1. INTRODUCTION Natural language provides a variety of devices for expressing relations between elements in a text.. Simply positioning two sentences in sequence conveys an implicit relation between them: (1) I bought a book. I'm going to read it on the plane. Clauses may also be joined with explicit lexical connectives: (2) I bought a book so that I could read it on the plane. A few relations may be expressed directly through particular types of subordination of one clause to another1: (3) I bought a book to read on the plane. This latter category is the most cohesive of these three devices, as the adjunct is crucially dependent on the material in the matrix clause for its interpretation (Halliday & Hasan, 1976). However, such structural linking mechanisms are also the most limited in applicability: only certain relations may be expressed 1 We refer here to infinitive clauses which are grammatically related to the main clause as optional adverbials rather than as complements (arguments) to a verb, such as "Floyd wanted to go to the zoo". in this way and complex grammatical constraints must be satisfied. In this paper, we analyze a particular class of structural devices, including the purpose clause (exemplified in 3 above), rationale clause, and infinitival relative, from the perspective of natural language generation. All three constructions express kinds of "purpose": purpose clauses express the use to which someone will put an object that is expressed in the main clause; rationale clauses express the overall intention behind the main clause action; infinitival relatives express the usual function of their NP head.2 We look at what underlying semantic relations license the constructions, the constraints on the syntactic form of the main and adjunct clauses, and the gapping pattern of the arguments of each adjunct. We discuss these as information needed by the generator in order for it to choose and use these devices correctly and discuss at what stages in the generation process the information must be applied. We contrast our analysis with those typically given from the perspective of generative- transformational linguistics, particularly thematic analyses, concluding that an analysis that considers the construction in a particular situation and in terms of a coherent model of the world can …

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