Quarterly (March, June, September, December)
160 pp. per issue
6 3/4 x 10
2014 Impact factor:

Computational Linguistics

Hwee Tou Ng, Editor
December 2009, Vol. 35, No. 4, Pages 559-595
(doi: 10.1162/coli.2009.35.4.35406)
© 2009 Association for Computational Linguistics
Binarization of Synchronous Context-Free Grammars
Article PDF (895.7 KB)

Systems based on synchronous grammars and tree transducers promise to improve the quality of statistical machine translation output, but are often very computationally intensive. The complexity is exponential in the size of individual grammar rules due to arbitrary re-orderings between the two languages. We develop a theory of binarization for synchronous context-free grammars and present a linear-time algorithm for binarizing synchronous rules when possible. In our large-scale experiments, we found that almost all rules are binarizable and the resulting binarized rule set significantly improves the speed and accuracy of a state-of-the-art syntax-based machine translation system. We also discuss the more general, and computationally more difficult, problem of finding good parsing strategies for non-binarizable rules, and present an approximate polynomial-time algorithm for this problem.