Structure-Driven Generation From Separate Semantic Representations

STRUCTURE-DRIVEN GENERATION FROM SEPARATE SEMANTIC REPRESENTATIONS Stephan Busernann Deutsches Forschungszentrum fiir Kfinstliche Intelligenz (DFKI) GmbH Stuhlsatzenhausweg 3, D-6600 Saarbrficken 11 uucp: buseman n@dfki.uni-sb.de ABSTRACT A new approach to structure-driven generation is I)resented that is based on a separate seman- tics as input structure. For the first time, a GPSG- based formalism is complemented with a system of pattern-action rules that relate the parts of a se- mantics to appropriate syntactic rules. This way a front end generator can be adapted to some ap- plication system (such as a machine translation system) more easily than would be possible with many previous generators based on modern gram- mar formalisms. 1 INTRODUCTION In the licld of unification-based computational linguistics, current research on tactical natural lan- guage (NL) generation concentrates on the folio- wing problem: i • Given a semantic representation (which is of- ten called logical form (LF)) and a grammar that includes a lexicon, what are the surface strings corresponding to the semantic repre- sentation? A variety of approaches to solving this problem in an efficient way has been put forward on the ba- sis of unification-based grammar formalisms with a context-free backbone and complex categories (for some discussion see e.g. [Shieber et al. 1990]). Most of this work shares a Montagovian view of seman- tics by assuming that LF be integrated into the grammar rules, thus assigning to each syntactic ca- tegory its semantic representation. Within this integrated-semantics approach the generation tmsk mainly consists of reconstructing a 1This work was partially funded by the German Mini- ster for Research trod Tedmology (BMFT) mt(ler contract ITW 9002. Most of the research underlying rids article was accomplished within the EURO'rH.A-D accompanying re- search project K IT-FAST at the Technical University of Ber- lin and fimded by the BMFT trader contract 1013211. I wish to thank Christa llauenschiid, John Nerbo[me, and Ilans Ilszk~weit h,r com,,lcntin g on earlier ve,.'~ions of this paper. given LF, thereby ensuring that the result is com- plete (all parts of the input structure are recon- structed) and coherent (no additional structure is built up). Thus, the surface strings then come out as a side effect. This paper describes a different use of seman- tics for generatio n. llere the semantics is not part of the grammar, but rather expressed within a se- parate semantic representation language (abbrcv.: SRL). This approach, in which the grammar only covers the syntax part, is called the separate se- mantics approach. It has a long tradition in At NL systems, but was rarely used for unification-based syntax and semantics. It will be argued that it can still be useful for interfacing a syntactic generator to some application system. The main goal of this paper is to describe a ge- nerator using a separate semantics and to suggest a structure-driven strategy that is bascd on a systcm of pattern-action (PA) rules, as they are known from AI production systems (for an overview see [Davis/King 1977]). The purpose of these rulcs is to explicitly relate the …

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