Language Technologies Institute; School of Computer Science; Carnegie Mellon University
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AUTHOR ADDR
5000 Forbes Ave., Pittsburgh, PA 15213
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ABSTRACT
Language model plays an important role in statistical machine translation systems. It is the key knowledge source to determine the right word order of the translation. Standard n-gram based language model predicts the next word based on the n − 1 immediate left context. Increasing the order of n and the size of the training data improves the performance of the LM as shown by the suffix array language model and distributed language model systems. However, such improvements narrow down very fast after n reaches 6. To improve the n-gram language model, we also developed dynamic n-gram language model adaptation and discriminative language model to tackle issues with the standard n-gram language models and observed improvements in the translation qualities. The fact is that human beings do not reuse long n-grams to create new sentences. Rather, we reuse the structure (grammar) and replace constituents to construct new sentences. Structured language model tries to model the structural information in natural language, especially the long-distance dependencies in a probabilistic framework. However, exploring and using structural information is computationally expensive, as the number of possible structures for a sentence is very large even with the constraint of a grammar. It is difficult to apply parsers on data that is different from the training data of the treebank and parsers are usually hard to scale up. In this