Learning and Inference for Hierarchically Split PCFGs

Slav Petrov, Dan Klein

Treebank parsing can be seen as the search for an optimally refined grammar consistent with a coarse training treebank. We describe a method in which a minimal grammar is hierarchically refined using EM to give accurate, compact grammars. The resulting grammars are extremely compact compared to other high-performance parsers, yet the parser gives the best published accuracies on several languages, as well as the best generative parsing numbers in English. In addition, we give an associated coarse-to-fine inference scheme which vastly improves inference time with no loss in test set accuracy.

Subjects: 13. Natural Language Processing; 13.3 Syntax

Submitted: Apr 26, 2007


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