Inner-Outer Bracket Models for Word Alignment using Hidden Blocks

Most of the best translation systems today are based on phrase translation pairs (i.e. “blocks”). The blocks are obtained from word alignment. In this paper, we use blocks to improve word alignment. Improved word alignment in turn leads to better inference of blocks. We propose two new probabilistic models and EM-based algorithms to estimate their parameters. The first model recovers IBM Model-1 as a special case. Both models outperform bidirectional alignments based on HMM or IBM Model-4: up to 10% absolute improvement in Chinese-English word alignment over GIZA Model-4 bidirectional alignment. Using blocks obtained from the proposed models, we also get statistically significant improvement in BLEU on NIST MT-03 test set.

By: Bing Zhao; Niyu Ge; Kishore Papineni

Published in: RC23491 in 2005


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