Compositional Semantics in Verbmobil

Compositional Semantics in Verbmobil Johan Bos Bj~irn Gamb~ick Christian Lieske Yoshiki Mori Manfred Pinkal Karsten Worm Department of Computational Linguistics University of the Saarland Postfach 151150 D-66041 Saarbrficken, Germany* e-mail : vm@coli .uni-sb.de Abstract The paper discusses how compositional semantics is implemented in the Verb- mobil speech-to-speech translation sys- tem using LUD, a description language for underspecified discourse representa- tion structures. The description lan- guage and its formal interpretation in DRT are described as well as its imple- mentation together with the architecture of the system's entire syntactic-semantic processing module. We show that a lin- guistically sound theory and formalism can be properly implemented in a sys- tem with (near) real-time requirements. 1 Introduction Contemporary syntactic theories are normally unification-based and commonly aim at specifying as much as possible of the peculiarities of specific language constructions in the lexicon rather than in the "traditional" grammar rules. When doing semantic interpretation within such a framework, we want a formalism which allows for • compositionality, • monotonicity, and • underspecification. Compositionality may be defined rather strictly so that the interpretation of a phrase always should be the (logical) sum of the interpreta- tions of its subphrases. A semantic formalism being compositional in this strict sense would also trivially be monotonic, since no destructive *This research was funded by the German Federal Ministry of Education, Science, Research, and Tech- nology (BMBF) under grant number 01 IV 101 R. changes would need to be undertaken while build- ing the interpretation of a phrase from those of its subphrases) However, compositionality is more commonly defined in a wider sense, allowing for other mappings from subphrase-to-phrase interpreta- tion than the sum, as long as the mappings are such that the interpretation of the phrase still is a function of the interpretations of the subphrases. A common such mapping is to let the interpre- tation of the phrase be the interpretation of its (semantic) head modified by the interpretations of the adjuncts. If this modification is done by proper unification, the monotonicity of the for- malism will still be guaranteed. In many applications for Computational Lin- guistics, for example when doing semantically based translation -- as in Verbmobil, the German national spoken language translation project de- scribed in Section 2 -- a complete interpretation of an utterance is not always needed or even desir- able. Instead of trying to resolve ambiguities, for example the ones introduced by different possible scopings of quantifiers, the interpretation of the ambiguous part is left unresolved. The semantic formalism of such a system should thus allow for the underspecification of these unresolved ambi- guities (but still allow for them to be resolved in a monotonic way, of course). An underspecified form representing an utterance is then the rep- resentation of a set of meanings, all the possible interpretations of the utterance. The rest of the paper is structured as follows. Section 2 gives an overview of the Verbmobil Project. Section 3 introduces LUD (description Language for Underspecified Discourse 'represen- tations), the semantic …

Content truncated to 500 words