Automatic Construction of Discourse Representation Structures

AUTOMATIC CONSTRUCTION OF DISCOURSE REPRESENTATION STRUCTURES Franz Guenthner Universit~it Tiibingen Wilhelmstr. 50 D-7400 Tdbingen, FRG Hubert Lehmann IBM Deutschland GmbH Heidelberg Scientific Center Tiergartenstr. 15 D-6900 Heidelberg, FRG Abstract Kamp's Discourse Representation Theory is a major breakthrough regarding the systematic translation of natural language discourse into logical form. We have therefore chosen to marry the User Specialty Languages System, which was originally designed as a natural language frontend to a relational database system, with this new theory. In the paper we try to show taking - for the sake of simplicity - Kemp's fragment of English how this is achieved. The re- search reported is going on in the context of the project Linguistics and Logic Based Legal Expert System undertaken jointly by the IBM Heidelberg Scientific Center and the Universit~it Tiibingen. 1 Introduction In this paper we are concerned with the systematic translation of natural language discourse into Dis- course Representation Structures as they are de- fined in Discourse Representation Theory (DRT) first formulated by Kamp (1981). This theory re- presents a major breakthrough in that it systemat- ically accounts for the context dependent interpretation of sentences, in particular with re- gard to anaphoric relations. From a syntactic point of view, however, Kamp chose a very restricted fragment of English. It is our goal, therefore, to extend the syntactic cover- age for DRT by linking it to the grammars described for the User Specialty Languages (USL) system (Lehmann (1978), Ott and Zoeppritz (1979), Leh- mann (1980), Sopefia (1982), Zoeppritz (1984)) which are comprehensive enough to deal with realis- tic discourses. Our main tasks are then to describe the syntactic framework chosen Discourse Representation Structures (DRSs) the translation from parse trees to DRSs The translation from parse trees to DRSs will, as we shall see, not proceed directly but rather via Inter- mediate Structures. which were already used in the USL system. Clearly, it is not possible here to de- scribe the complete process in full detail. We will hence limit ourselves here to a presentation Kamp's fragment of English in our framework. The work reported here forms part of the devel- opment of a Natural Language Analyzer that will translate natural language discourse into DRSs and that is evolving out of the USL system. We intend to use this Natural Language Analyzer as a part of a legal expert system the construction of which is the objective of a joint project of the University of Tiibingen and the IBM Heidelberg Scientific Center. 2 SyntaJc 2.1 Syntactic framework and parsing process The parser used in the Natural Language Analyzer was originally described by Kay (1967) and subse- quently implemented in the REL system (Thompson et. al. (1969)). The Natural Language Analyzer uses a modified version of this parser which is due to Bertrand &al (1976, IBM (1981)). Each grammar rule contains the name of an inteP- pretation routine, and hence each node in the parse tree for a given sentence also contains the name of such a routine. The semantic …

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