Semantic-based Transfer

Semantic-based Transfer* Michael Dorna and Martin C. Emele Institut fiir Maschinelle Sprachverarbeitung Azenbergstralle 12 D-70174 Stuttgart {dorna, emele} @ims. uni-stuttgart, de Abstract This article presents a new semantic- based transfer approach developed and applied within the Verbmobil Machine Translation project. We give an overview of the declarative transfer formalism to- gether with its procedural realization. Our approach is discussed and compared with several other approaches from the MT literature. The results presented in this article have been implemented and integrated into the Verbmobil system. 1 Introduction The work presented in this article was developed within the Verbmobil project (Kay et al., 1994; Wahlster, 1993). This is one of the largest projects dealing with Machine Translation (MT) of spo- ken language. Approxinmtely 100 researchers in 29 public aad industrial institutions are involved. The application domain is spontaneous spoken language in face-to-face dialogs. The current sce- nario is restricted to the task of appointment scheduling and the languages involved are English, German and Japanese. This article describes the realization of a trans- fer approach based on the proposals of (Abb and Buschbeck-Wolf, 1995; Caspari and Schmid, 1994) and (Copestake, 1995). Transfer-based MT 1, see e.g. (Vauquois and Boi~et, 1985; Nagao et al., 1985), is based on con~rastive bilingual corpus analyses from which a bilingual lexicon of trans- fer equivalences is derived. In contrast to a purely *This work was funded by the German Federal Ministry of Education, Science, Research and Tech- nology (BMBF) in the framework of the Verbmobil project under grant 01 IV 101 U. We would like to thank our colleagues of the Verbmobil subproject Transfer, our IMS colleagues Ulrich Heid and C.J. Rupp and our anonymous reviewers for usefltl feed- back a~ld discussions on earlier drafts of the paper. The responsibility for the contents of this paper lies with the authors. 1For a more detailed overview of different ap- proaches to MT, see e.g. (Hutchins and Solners, 1992). lexicalist approach which relates bags of lexical signs, as in Shake-and-Bake MT (Beaven, 1992; Whitelock, 1992), our transfer approach operates on the level of semantic representations produced by various analysis steps. The output of transfer is a semantic representation for the target language which is input to the generator and speech synthe- sis to produce the target language utterance. Our transfer equivalences abstract away from morpho- logical and syntactic idiosyncracies of source and target languages. The bilingual equivalences are described on the basis of semantic representations. Since the Verbmobil domain is related to dis- course rather than isolated sentences the model theoretic semantics is based on Kamp's Discourse Representation Theory, DRT (Kamp and Reyle, 1993). In order to allow for underspecification, variants of Underspecified Discourse Representa- tion Structures (UDRS) (Reyle, 1993) are em- ployed as semantic formalisms in the different analysis components (Bos et al., 1996; Egg and Lebeth, 1995; Copestake et al., 1995). Together with other kinds of information, such as tense, aspect, prosody and morpho-syntax, the different semantic representations are mapped into a single multi-dimensional representation called Verbmobil Interface …

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