TAILIEUCHUNG - Báo cáo khoa học: "Discriminative Training and Maximum Entropy Models for Statistical Machine Translation"

We present a framework for statistical machine translation of natural languages based on direct maximum entropy models, which contains the widely used source-channel approach as a special case. All knowledge sources are treated as feature functions, which depend on the source language sentence, the target language sentence and possible hidden variables. This approach allows a baseline machine translation system to be extended easily by adding new feature functions. We show that a baseline statistical machine translation system is significantly improved using this approach. . | Proceedings of the 40th Annual Meeting of the Association for Computational Linguistics ACL Philadelphia July 2002 pp. 295-302. Discriminative Training and Maximum Entropy Models for Statistical Machine Translation Franz Josef Och and Hermann Ney Lehrstuhl fur Informatik VI Computer Science Department RWTH Aachen - University of Technology D-52056 Aachen Germany och ney @ Abstract We present a framework for statistical machine translation of natural languages based on direct maximum entropy models which contains the widely used source-channel approach as a special case. All knowledge sources are treated as feature functions which depend on the source language sentence the target language sentence and possible hidden variables. This approach allows a baseline machine translation system to be extended easily by adding new feature functions. We show that a baseline statistical machine translation system is significantly improved using this approach. 1 Introduction We are given a source French sentence fJ fa . fj . fj which is to be translated into a target English sentence el el . 6i . ei. Among all possible target sentences we will choose the sentence with the highest probability 1 e argmax Pr el fJ 1 fa The argmax operation denotes the search problem . the generation of the output sentence in the target language. 1The notational convention will be as follows. We use the symbol Pr to denote general probability distributions with nearly no specific assumptions. In contrast for model-based probability distributions we use the generic symbol p . . Source-Channel Model According to Bayes decision rule we can equivalently to Eq. 1 perform the following maximization el argmax Pr el Pr fJ ef 2 ei e1 This approach is referred to as source-channel approach to statistical MT. Sometimes it is also referred to as the fundamental equation of statistical MT Brown et al. 1993 . Here Pr el is the language model of the target language whereas Pr fJ el

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