Combining Functionality and Object-Orientedness for Natural Language Processing

Combining Functionality and Ob]ec~Orientedness for Natural Language Processing Toyoakl Nishida I and Shuji Doshita Department of Information Science, Kyoto University Sakyo-ku, Kyoto 606, JAPAN Abstract This paper proposes a method for organizing linguistic knowledge in both systematic and flexible fashion. We introduce a purely applicative language (PAL) as an intermediate representation and an object-oriented computation mechanism for its interpretation. PAL enables the establishment of a principled and well-constrained method of interaction among lexicon-oriented linguistic modules. The object-oriented computation mechanism provides a flexible means of abstracting modules and sharing common knowledge. 1. Introduction The goal of this paper is to elaborate a domain-independent way of organizing linguistic knowledge, as a step forwards a cognitive processor consisting of two components: a linguistic component and a memory component. In this paper we assume the existence of the latter component meeting the requirements described in [Schank 82]. Thus the memory component attempts to understand the input in terms of its empirical knowledge, predict what happens next, and reorganize its knowledge based on new observations. Additionally, we assume that the memory component can judge whether a given observation is plausible or not, by consulting its empirical knowledge. The role of the linguistic component, on the other hand, is to supply "stimulus" to the memory component. More specifically, the linguistic component attempts to determine the propositional content, to supply missing constituents for elliptical expressions, to resolve references, to identify the focus, to infer the intention of the speaker, etc. In short, the role of the [iguistic component is to "translate" the input into an internal representation. For example, the output of the linguistic component for an input: When did you go to New York? is something like the following2: There is an event e specified by a set of predicates: isa(e)=going A past(e) A agent(e)=the_hearer A destination(e)=New_York. The speaker is asking the hearer for the time when an event e took place. The hearer presupposes that the event e actually took place at some time in the past. 1Currently visiting Department of Computer Science, Yale University, New Haven, Connecticut 06520, USA. If the presupposition contradicts what the memory component knows, then the memory component will recognize the input as a loaded question [Kaplan 82]. As a result, the memory component may change its content or execute a plan to informing the user that the input is inconsistent with what it knows. The primary concern of this paper is with the linguistic component. The approach we take in this paper is to combine the notion of eompositionality a and an object-oriented computational mechanism to explore a principled and flexible way of organizing linguistic knowledge. 2. Intermediate Representation and Computational Device for Interpretation 2.1 PAL (Purely Applicative Language) Effective use of intermediate representations is useful. We propose the use of a language which we call PAL (Purely Applicative Language). In PAL, new composite expressions are constructed only with a binary form of function application. Thus, if z and I/ are well-formed formulas of PAL, so is a form …

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