SAUMER: Sentence Analysis Using Metarules

SAUMER: SENTENCE ANALYSIS USING METARULES Fred Popowich Natural Language Group Laboratory for Computer and Communications Research Department of Computing Science Simon Fraser University Burnaby. B.C.. CANADA V5A 1S6 ABSTRACT The SAUMER system uses specifications of natural language grammars, which consist of rules and metarules. to provide a semantic interpretation of an input sentence. The SAUMER ' Specification Language (SSL) is a programming language which combin~ some of the features of generalised phrase structure grammars (Gazdar. 1981 ). like the correspondence between syntactic and semantic rules, with definite clause grammars (DCC-s) (Pereira and Warren. 1980) to create an executable grammar specification. SSL rules are similar to DCG rules except that they contain a semantic component and may also be left recursive. Metarules are used to generate new rules trom existing rules before any parsing is attempted. A.n implementation is tested which can provide semantic interpretations for sentences containing tepicalisation, relative clauses, passivisation, and questions. 1. INTRODUCTION The SAUMER system allows the user to specify a grammar for a natural language using rules and metarules rhts grammar can then be u¢,ed ~ obtain a semantic interpretation of an input sentence. The SAUMER Specification language (SSL). which L~ a variation of definite clause gr~s (DCGs) (Pereira and Warren. 1980). captures some ,ff the festures of generaI£.ted phrase structure grammar5 (GPSGs) (Gazdax, 1981) (GaTrl~r and Pullum. 1982). like rule schemata, rule transformations. structured categories, slash categories, and the correspondence between syntactic and semantic rules. The semantics currently used in the system are based on Schubert and Pelletiers description in (Schubert and Pelletier. 1982). - which adapts the intetmional logic intervretation associated with GPSGs. into a more conventional logical notation 2. THE SEMANTIC LOGICAL NOTATION The logical notation associated with the gr~mm~r differs from. the usual notation of intensional logic_since it captures some intmtive aspects of natural language, l Thus. individuals and objects are treated as entities. instead of collections of prope'rties, and actions are n-ary relations between these entities. Many of the problems that the intensional notation would solve are handled by allowing ambiguity to be represented in the logical notation. Consequently. as is common in other approaches. (e.g.. Gawron. 1982). much of the processing is deferred to the pragmatic stage. The structure of the lexicon, and the appearance of post processing markers (sharp angle brackets) are designed to reflect this ambiguity. The lexicon is organised into two levels. For the semantic interpretation, the first level gives each word a tentative interpretation. During the pragmatic analysis, more complete processing information will result in the final interpretation being obtained from the second level of the lexicon. For e~mple, the sentence John misses John could be given an initial interpretation of: (2.1) [ Johnl misa2 John3 ] with Johnl, miss2 and John3 obtained from the first level of the two level lexicon. The pragmatic stage will determine if Johal and John3 both refer to the same entry, say JOHN SMITH1. of the second level of the lexicon, or if they correspond to different entries, say JOHN_JONES1 …

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