Designer Definites in Logical Form

DESIGNER DEFINITES IN LOGICAL FORM Mary P. Harper* School of Electrical Engineering Purdue University West Lafayette, IN 47907 Abstract In this paper, we represent singular definite noun phrases as functions in logical form. This represen- tation is designed to model the behaviors of both anaphoric and non-anaphoric, distributive definites. It is also designed to obey the computational con- straints suggested in Harper [Har88]. Our initial representation of a definite places an upper bound on its behavior given its structure and location in a sentence. Later, when ambiguity is resolved, the precise behavior of the definite is pinpointed. 1 Introduction A goal of natural language research is to provide a computer model capable of understanding En- glish sentences. One approach to constructing this model requires the generation of an unambiguous internal representation for each sentence before at- tempting to represent subsequent sentences. Natu- ral language systems that attempt to guess the in- tended meaning of a sentence without considering subsequent sentences usually make no provision for recovery from incorrect guesses since that would re- quire storing information about the ambiguity of the sentence. Hence, this approach may require the pro- cessing of several sentences before enough informa- tion is available to determine the intended meaning of the sentence being represented. However, in or- der to make the inferences necessary to resolve some ambiguities, some internal representation is needed for both the current sentence as well as subsequent sentences. A more powerful approach is to leave the ambiguity unresolved in an intermediate repre- sentation until the necessary information has been processed. We adopt this second approach, which advocates mapping parsed sentences into an inter- mediate level of representation called logical form *This paper contains results from the author's the- sis in the Computer Science Department at Brown Uni- versity. The paper has benefited from discussions with Eugene Charniak, Kate Sanders, Leora Morgenstern, Tom Dean, Paul Harper and Frederic Evans. The work was supported in part by the NSF grants IST 8416034 and IST 8515005, ONR grant N00014-79-C-0529, and AFOSR grant F49620-88-c-0132. 62 [SP84; All87; Har88]. Logical form partially spec- ifies the meaning of a sentence based on syntactic and sentence-level information, without considering the effect ofpragmatics and context. Later, as more information becomes available, the representation of the sentence is incrementally updated until all am- biguities have been resolved. In the literature, two sources of ambiguity have been handled using logical form, quantifier scop- ing (see [SP84; Al187]) and pronoun resolution (see [Har88; Har90]). In this paper, we will discuss the use of logical form for handling the ambiguities in the meanings of singular definite noun phrases. But first, it will be useful to briefly review the logical form for pronouns. 2 Pronouns in Logical Form Pronouns are a source of underspecification in a sen- tence which can be handled in logical form. The antecedent of a pronoun cannot be immediately de- termined when the sentence containing it is parsed. Contextual and syntactic constraints combine to al- low a listener/reader to decide …

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