Speaker: Dr. Hao Zhang (Google Research)
Title: Efficient Higher-Order Dependency Parsing with Cube Pruning
Date: Friday 3/8
Place: Graduate Center Room 6496, 5th Ave & 34th St.
State-of-the-art graph-based parsers use features over higher-order dependencies that rely on decoding algorithms that are slow and difﬁcult to generalize. On the other hand, transition-based dependency parsers can easily utilize such features without increasing the linear complexity of the shift-reduce system beyond a constant. We attempt to address this imbalance for graph-based parsing by generalizing the Eisner (1996) algorithm to handle arbitrary features over higher-order dependencies. The generalization is at the cost of asymptotic efﬁciency. To account for this, cube pruning for decoding is utilized (Chiang, 2007). For the ﬁrst time, label tuple and structural features such as valencies can be scored efﬁciently with third-order features in a graph-based parser. Our parser achieves the state-of-art unlabeled accuracy of 93.06% and labeled accuracy of 91.86% on the standard test set for English, at a faster speed than a re-implementation of the third-order model of Koo et al. (2010).
Hao Zhang is a senior software engineer at Google, working on parsing and syntax-based machine translation. He received his PhD degree in Computer Science from the University of Rochester in 2008, his master's degree from the Chinese Academy of Sciences in 2003, and his bachelor's degree from Peking University in 2000. He has published fifteen articles in ACL/EMNLP/Coling and the journal of Computational Linguistics on the topics of synchronous grammars, efficient decoding algorithms, word alignment, and dependency parsing.