tailieunhanh - Báo cáo khoa học: "Dynamic Programming for Linear-Time Incremental Parsing"

Incremental parsing techniques such as shift-reduce have gained popularity thanks to their efficiency, but there remains a major problem: the search is greedy and only explores a tiny fraction of the whole space (even with beam search) as opposed to dynamic programming. | Dynamic Programming for Linear-Time Incremental Parsing Liang Huang USC Information Sciences Institute 4676 Admiralty Way Suite 1001 Marina del Rey CA 90292 lhuang@ Kenji Sagae USC Institute for Creative Technologies 13274 Fiji Way Marina del Rey CA 90292 sagae@ Abstract Incremental parsing techniques such as shift-reduce have gained popularity thanks to their efficiency but there remains a major problem the search is greedy and only explores a tiny fraction of the whole space even with beam search as opposed to dynamic programming. We show that surprisingly dynamic programming is in fact possible for many shift-reduce parsers by merging equivalent stacks based on feature values. Empirically our algorithm yields up to a five-fold speedup over a state-of-the-art shift-reduce dependency parser with no loss in accuracy. Better search also leads to better learning and our final parser outperforms all previously reported dependency parsers for English and Chinese yet is much faster. 1 Introduction In terms of search strategy most parsing algorithms in current use for data-driven parsing can be divided into two broad categories dynamic programming which includes the dominant CKY algorithm and greedy search which includes most incremental parsing methods such as Both have pros and cons the former performs an exact search in cubic time over an exponentially large space while the latter is much faster in linear-time and is psycholinguistically motivated Frazier and Rayner 1982 but its greedy nature may suffer from severe search errors as it only explores a tiny fraction of the whole space even with a beam. Can we combine the advantages of both approaches that is construct an incremental parser McDonald et al. 2005b is a notable exception the MST algorithm is exact search but not dynamic programming. that runs in almost linear-time yet searches over a huge space with dynamic programming Theoretically the answer is negative as Lee 2002 shows .

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