Deriving Database Queries from Logical Forms by Abductive Definition Expansion

Deriving Database Queries from Logical Forms by Abductive Definition Expansion Manny Rayner and Hiyan Alshawi * SRI International Cambridge Computer Science Research Centre 23 Millers Yard, Cambridge CB2 1RQ, U.K. manny©cam, sri. com hiyan~cam, sri. tom Abstract The paper describes a principled approach to the problem of deriving database queries from logical forms produced by a general NL in- terface. Our method attempts to construct a database query and a set of plausible assump- tions, such that the logical form is equivalent to the query given the assumptions. The do- main information needed is provided as declar- ative meaning postulates, including "defini- tional equivalences". The technical basis for the approach is that a "definition" of the form Head A Conditions ~ Body can be read pro- cedurally as "Expand Head to Body if it oc- curs in an environment where Conditions can be inferred". The "environment" is provided by the other conjuncts occurring together with Head in the original logical form, together with other meaning postulates and the contents of the database. The method has been imple- mented in CLARE, a language and reasoning system whose linguistic component is the SRI Core Language Engine. 1 Introduction The basic question addressed in this paper is that of how to connect a general NL interface and a back-end application in a principled way. We will assume here that the interface takes input in a natural language and produces a representation in some kind of enriched first- order logic, and that the application is some kind of rela- tional database; this is a common and important situa- tion, and it is well-known that the problems involved are non-trivial. The techniques used apply equally well to other NLP applications which involve mapping linguistic concepts to knowledge base predicates. Concrete exam- ples in the paper will be taken from the SRI CLARE system, working in the domain of project resource man- agement. CLARE is a combined natural language and *CLARE is being developed as part of 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 Department of Trade and Industry. reasoning system which includes the Core Language En- gine (or CLE, Alshawi 1992) as its language component. The CLE produces semantic interpretations of sentences in a notation called Quasi Logical Form. For database interface applications, the semantic interpretations are converted into fairly conventional logical forms before query derivation takes place. A NL interface like CLARE which is general (rather than being tailored to the application) will produce log- ical forms that essentially mirror the linguistic content of the input. It will thus normally contain what might be called "linguistic" predicates (i.e. word senses): for example, the logical form for a query like ($1) List all payments made to BT during 1990. would be expected to contain predicates corresponding directly to payment, make and during. An appropriate database query, on the other hand, might be a …

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