A Foundation for Semantic Interpretation

A FOUNDATION FOR SEMANTIC INTERPRETATION Graeme Hirst Department of Computer Science Brown University Providence, RI 02912 Abstract Traditionally, translation from the parse tree repre- senting a sentence to a semantic representation (such as frames or procedural semantics) has a/ways been the most ad hoc part of natural language understand- •ng (NLU) systems. However, recent advances in lin- guistics, most notably the system of formal semantics known as Montague semantics, suggest ways of putting NLU semantics onto a cleaner and firmer foundation. We are using a Montague-inspired approach to seman- tics in an integrated NL U and pro blem-solving system that we are building. Like Montague's, our semantics are compositional by design and strongly typed, with semantic rules in one-to-one correspondence with the meaning-affecting rules of a Marcus-style parser. We have replaced Montague's semantic objects, functors and truth conditions, with the elements of the frame language Frail, and added a word sense and case slot disambiguation system. The result is a foundation for semantic interpretation that we believe to be superior ~o previous approaches. I. Introduction By semantic interpretation we mean the process of mapping from a syntactically analyzed sentence of natural language to a representation of its meaning. We exclude from semantic interpretation any con- sideration of discourse pragmatics; rather, discourse pragmatics operate upon the output of the semantic interpreter. We also exclude syntactic analysis; the integration of syntactic and semantic analysis becomes very messy when complex syntactic constructions are considered, and, moreover, it is our observation that those who argue for the integration of the two are usually arguing for subordinating the role of syntax, a position we reject. This is not to say that parsing can get by without semantic help; indirect object finding, This work was supported by the Oflfice of Naval Research under contract number N00014-79-C-0592. and prepositional phrase and relative clause attach- ment, for example, often require semantic knowledge. Below we will show that syntax and semantics may work well together while remaining distinct modules. Research on semantic interpretation in artificial intelligence goes back to Woods's dissertation (1967, 1968), which introduced procedural semantics in a natural-language front-end for an airline reservation system. Woods's system had rules with patterns that, when they matched part of the parsed input sentence, contributed a string to the semantic representation of the sentence. This string was usually constructed from the terminals of the matched parse tree frag- ment. The strings were combined to form a procedure call that, when evaluated, entered or retrieved the ap- propriate database information. This approach is still the predominant one today, and even though it has been refined over the years, semantic interpretation remains perhaps the least understood and most ad hoc area of natural language understanding (NLU).I However, recent advances in linguistics, most not- ably Montague semantics (Montague 1973; Dowry, Wall and Peters 1981), suggest ways of putting NLU semantic interpretation on a cleaner and firmer foun- dation than it now is. In this paper, we describe such a foundation. 2 2. Montague semantics …

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