Policy Gradient as a Proxy for Dynamic Oracles in Constituency Parsing

ACL 2018

Policy Gradient as a Proxy for Dynamic Oracles in Constituency Parsing

Jan 28, 2021
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Abstract: Dynamic oracles provide strong supervision for training constituency parsers with exploration, but must be custom defined for a given parser’s transition system. We explore using a policy gradient method as a parser-agnostic alter-native. In addition to directly optimizing for a tree-level metric such as F1, policy gradient has the potential to reduce exposure bias by allowing exploration during training; moreover, it does not require a dynamic oracle for supervi-sion. On four constituency parsers in three languages, the method substantially outperforms static oracle likelihood training in almost all settings. For parsers where a dynamic oracle is available (including a novel oracle which we define for the transition system of Dyer et al., 2016), policy gradient typically recaptures a substantial fraction of the performance gain afforded by the dynamic oracle. Authors: Daniel Fried, Dan Klein (University of California, Berkeley)

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