Monotonic Semantic Interpretation

MONOTONIC SEMANTIC INTERPRETATION* Hiyan Alshawi and Richard Crouch SRI International Cambridge Computer Science Research Centre 23 Millers Yard Cambridge CB2 1RQ, U.K. hiyan~cam, sri. corn rc~cam, sri. corn ABSTRACT Aspects of semantic interpretation, such as quan- tifier scoping and reference resolution, are often realised computationally by non-monotonic opera- tions involving loss of information and destructive manipulation of semantic representations. The paper describes how monotonic reference resolu- tion and scoping can be carried out using a re- vised Quasi Logical Form (QLF) representation. Semantics for QLF are presented in which the de- notations of formulas are extended monotonically as QLF expressions are resolved. 1. INTRODUCTION The monotonicity property of unification based grammar formalisms is perhaps the most impor- tant factor in their widespread use for grammatical description and parsing. Monotonicity guarantees that the grammatical analysis of a sentence can proceed incrementally by combining information from rules and lexical entries in a nondestructive way. By contrast, aspects of semantic interpreta- tion, such as reference and quantifier scope reso- lution, are often realised by non-monotonic opera- tions involving loss of information and destructive manipulation of semantic representations. A 'two- level' approach to semantic interpretation tends to result (Bronneberg el al. 1980), where an initial, underspecified representation is transformed into a separate, specified, representation. The goal of the work described here is to pro- vide a model for semantic interpretation that is fully monotonic in both linguistic and contextual aspects of interpretation, and which employs just one level of semantic representation -- Quasi Log- ical Form (QLF). Contextual resolution of under- *This work on the Core Language Engine was carried out under CLARE, a collaborative project involving BP Research, British Aerospace, British Telecom, Cambridge University, SRI International and the UK Defence Research Agency. The project is funded in part by the UK Depart- ment of Trade and Industry. specified QLF expressions involves the instantia- tion of QLF meta-variables. The semantics for the QLF formalism makes the denotation of a QLF formula a partial function to truth-values, with resolution leading to a monotonic extension of the denotation function. We believe that there are several advantages to the approach taken, includ- ing: • Order independence of resolution operations • Production of partial interpretations • Simpler interactions between phenomena • Reversibility for synthesis/generation The QLF formalism is a development of Alshawi 1990. As before, underspecified QLFs are pro- duced on the basis of a unification grammar. Pre- viously, QLF resolution was only partially mono- tonic; full monotonicity required changes to the original QLF formalism and the resolution and scoping processes. These changes have been im- plemented in a further development of the Core Language Engine (Alshawi 1992), although we will ignore most implementation issues in the present paper. The paper is organized as follows. Section 2 provides the syntax of the QLF language and Sec- tion 3 gives some illustrative examples of mono- tonic QLF resolution. Sections 4 and 5 present the semantics of the QLF formalism. Section 6 dis- cusses the relationship between monotonic inter- pretation, …

Content truncated to 500 words