Translation by Quasi Logical Form Transfer

The paper describes work on applying a general purpose natural language processing system to transfer-based interactive translation. Transfer takes place at the level of Quasi Logical Form (QLF), a contextually sensitive logical form representation which is deep enough for dealing with cross-linguistic differences. Theoretical arguments and experimental results are presented to support the claim that this framework has good properties in terms of modularity, compositionality, reversibility and monotonicity. 1 I N T R O D U C T I O N In this paper we describe a translation project whose aim is to build an experimental Bilingual Conversation Interpreter (BCI) which will allow communication through typed text between two monolingual humans using different languages (of Miike et al, 1988). The choice of languages for the prototype system is English and Swedish. Input sentences are analysed by the Core Language Engine (CLE 1) as far as the level of Quasi Logical Form (QLF; Alshawi, 1990), and then, instead of further ambiguity resolution, undergo transfer into another QLF having constants and predicates corresponding to word senses in the other language. The transfer rules used in this process correspond to a certain kind of meaning postulate. The CLE then generates an output, sentence from the target 1 Tile CLE is described in Alshawi (1991) which includes more detailed discussion of the BCI architecture in a chapter by the present, authors, language QLF, using the same linguistic data as is used for analysis of that language. QLFs were selected as the appropriate level for transfer because they are far enough removed from surface linguistic form to provide the flexibility required by cross-linguistic differences. On the other hand, the linguistic, unification-based processing involved in creating them can be carried out efficiently and without the need to reason about the domain or context; the QLF language has constructs for explicit representation of contextually sensitive aspects of interpretation. When it is necessary, for correct translation, to resolve an ambiguity present at QLF level, the BCI system interacts with the source language user to make the necessary decision, asking for a choice between word sense paraphrases or between alternative partial bracketings of the sentence. There • is thus a strong connection between our choice of a representation sensitive to context and the use of interaction to resolve context dependent ambiguities, but in this paper we concentrate on representational and transfer issues. 2 C L E R E P R E S E N T A T I O N L E V E L S In this section we explain how QLF fits into the overall architecture of the CLE and in section 3 we discuss the reasons for choosing it for interactive dialogue translation.