Another Look at Nominal Compounds

ANOTHER LOOK AT NOMINAL COMPOUNDS Pierre Isabelle D~partement de linguistique Universit~ de Montreal C.P. 6128, Succ. A, Montreal, Qua., Canada H)C )37 ABSTRACT We present a progress report on our research on nominal compounds (NC's). Recent approaches to this probiem in linguistics and natural ianguage processing (NLP) are reviewed and criticized. We argue that the notion of "roie nominal", which is at the interface of linguistic and extraiinguis- tic knowledge, is crucial for characterizing NC'e as weII as other Iinguistic phenomena. We examine a number of constraints on the semantic interpre- tation ruies for NC's. Proposals are made that shouid improve the capability of NLP systems to deaI with NC's. I INTRODUCTION A. Problem Statement As a first approximation, we define a "nominal compound (NC) as s string of two or more nouns having the same distribution as a singie noun, as in example (I): (1) aircraft bomb bay door actuating cylinders We will see below that provisions have to be made in some cases for intervening adjectives. NC's can exhibit various degrees of lexica- lization, but we will focus our attention on productive rules for forming novel compounds. As to their surface syntax, NC's can assume any structure generated by the rule N --> N N; accor- dingly, their structural ambiguity grows exponen- tially with their length (following the "Catalan sequence"). How, then, do we determine that the normal interpretation for (i) imposes the bracke- ting shown in (2), rather than any of the other 41 syntactically possible bracketings? (2) ((aircraft ((bomb bay) door)) (actuating cylinder)) B. Goal__ssof th___ee study We believe that the analysis of NC's repre- sents an important and largely unsolved problem. From a theoretical point of view this problem raises the question of how to deal with noun semantics. And since noun meaning appears to be closely connected with knowledge of the world, one is led to explore the modes of interaction between linguistic and conceptual knowledge. From an NLP perspective, NC's have turned out to be an important stumbling block for sys- tems that attempt to deaI with real-iife text, especiaIly in technical domains, for purposes such as machine translation (IsabeIle, to appear), information retrieval, etc. Our ultimate goal is to develop an NLP sys- tem capable of analyzing large classes of NC's in the sublanguage (Kittredge and Lehrberger, i982) of aircraft maintenance manuals. We do not aim at solving all cases, since we believe the problem to be exceedingly difficult. At the present stage of our inquiry, we concentrate on the design of s suitable theoretical framework. In section II, we present a brief review of previous work in linguistics and NLP. In sections III and IV, we examine two aspects of the seman- tics of nouns that are crucially relevant to the analysis of NC's: predicative nouns and role nominals. Finally, in section V, we explore pos- sible constraints on the semantic interpretation of NC's. II BACKGROUND A. Approaches in Linguistics The early study of Lees (1963) classified NC's on purely grammatical …

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