A New Method Based on Context for Combining Statistical Language Models

摘要

In this paper we propose a new method to extract from a corpus the histories for which a given language model is better than another one. The decision is based on a measure stemmed from perplexity. This measure allows, for a given history, to compare two language models, and then to choose the best one for this history. Using this principle, and with a 20K vocabulary words, we combined two language models: a bigram and a distant bigram. The contribution of a distant bigram is significant and outperforms a bigram model by 7.5%. Moreover, the performance in Shannon game are improved. We show through this article that we proposed a cheaper framework in comparison to the maximum entropy principle, for combining language models. In addition, the selected histories for which a model is better than another one, have been collected and studied. Almost, all of them are beginnings of very frequently used French phrases. Finally, by using this principle, we achieve a better trigram model in terms of parameters and perplexity. This model is a combination of a bigram and a trigram based on a selected history.