Translation by Abduction
SRI INTERNATIONAL MENLO PARK CA ARTIFICIAL INTELLIGENCE CENTER
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Many existing approaches to machine translation take for granted that the information presented in the output is found somewhere in the input, and, moreover, that such information should be expressed at a single representational level, for example, in terms of the parse trees or of semantic assertions. Languages, however, not only express the equivalent information by drastically different linguistic means, but also often disagree in what distinctions should be expressed linguistically at all. For example, in translating from Japanese to English, it is often necessary to supply determiners for noun phrases, and this in general cannot be done without deep understanding of the source text. Similarly, in translating from English to Japanese, politeness considerations, which in English are implicit in the social situation and explicit in very diffuse ways in, for example, the heavy use of hypotheticals, must be realized grammatically in Japanese. Machine translation therefore requires that the appropriate inferences be drawn and that the text be interpreted to some depth see Oviatt, 1988. Recently, an elegant approach to inference in discourse interpretation has been developed at a number of sites e.g., Hobbs et al., 1988 Charniak and Goldman, 1988 Norvig, 1987, all based on the notion of abduction, and we have begun to explore its potential application to machine translation. We argue that this approach provides the possibility of deep reasoning and of mapping between the languages at a variety of levels See also Kaplan et al., 1988, on the latter point. Abductive inference is inference to the best explanation. The easiest way to understand it is to compare it with two words it rhymes with-deduction and induction. Much of the way we interpret the world in general can be understood as a process of abduction.