Backward Beam Search Algorithm for Dependency Analysis of Japanese

Backward beam search for dependency analysis of Japanese is proposed. As dependencies normally go from left to right in Japanese, it is effective to analyze sentences backwards (from right to left). The analysis is based on a statistical method and employs a beam search strategy. Based on experiments varying the beam search width, we found that the accuracy is not sensitive to the beam width and even the analysis with a beam width of 1 gets almost the same dependency accuracy as the best accuracy using a wider beam width. This suggested a deterministic algorithm for backwards Japanese dependency analysis, although still the beam search is effective as the N-best sentence accuracy is quite high. The time of analysis is observed to be quadratic in the sentence length.