A Tool for Collecting Domain Dependent Sortal Constraints From Corpora

A TOOL FOR COLLECTING DOMAIN DEPENDENT SORTAL CONSTRAINTS FROM CORPORA Frangois Andry*, Marl( Gawron, John Dowding, and Robert Moore SRI International, Menlo Pmq% CA *CAP GEMINI Innovation, Boulogne I:lilla.ncourt, France Internet: andry@capsogeti.fi: Topical paper : Tools for NL Understanding (Portability). 1 ABSTRACT In this paper, we describe a tool designed to gener- ate semi-automatically the sortal constraints spe- cific to a domain to be used in a natural language (NL) understanding system. This tool is evaluated using the Sll,I Gemini NL understanding system in tile ATIS domain. of work we put into the first domain application 1. In this paper, we describe tile results of us- ing this semi-automatic tool to port the (',e, udlii NL system to the ATIS domahi, a (lomltin that (ienlini had ah'eady been ported to, arid for which it ]lad achiew~,d high perl'orluance ~ttld gi'al'l-illiati- cal coverage using hand-written sortal constraints. Chossing a known domain, rather than a new one, allowed us to compare tile performance of tile de- rived sorts to the hand-written ones, holding the domain, grammar, and lexicon constant. It also allowed us to evahlate the selni-~ultoma.tically ob- tained cown'age using the ewduation tools pro- vided for the A'I?IS corpus. 2 INTRODUCTION The construction of a knowledge base related to a specific domain for a NL understanding system is time consuming. In the Gemini system, the domain-specific knowledge base includes a sort hi- erarchy and a set ot" sort rules tha~ provide (largely domain-specific) selectional restrictions for ew~ry predicate invoked by the lexicon and the gram- mar. The selectional restrictions provide a source of constraints over and above syntactic constraints for choosing the correct analysis of a sentem:e. The sort rules are generally entered by a linguist, by hand, from the study of a corpus and while tuning the grammar. IIowever, the use of an interactiw; tool that can help the linguist to acquire this knowledge from a corpus[a][5], can drastically reduce the time dedicated to this task, and also improve the qual- ity of the knowledge base in terms of both ac- curacy and conipleteness. 'l'he reduction in the amount of etfort to develop the knowledge base becomes obvious when porting an existing system to a new domain. At SR,I, our main concern was to port Gemini, our NL understanding system to other domains without investing the same amount 3 PARSING WITH SORTS Gemini[2] implements a clear separation Imtween syntactic and sem~mtic information. Each syntac- tic node invokes a set of semantic rules which re- sult in the bnihling of a set of logical forms for that node. Selectlomd restrictions are enforced on the logical fornls through the sorts nlechanism: All prcdlcations in :~ catldiihd.e logical form IlallSt I)e li- censed by some sorts rule. The sorts are located in ~ conceptual hierarchy of approxhmd;cly 200 con- cepts mid are imphmleiH.ed as Pro]og terms such that nlol'e gellorai sorts SllltSllllle lliore specific sorts[6]. Failure to match any available sorts rule can thus he implernented as unification-failure. Gemini parser creates logical forms …

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