Learning and inference for hierarchically split PCFGs
Slav Petrov, Dan Klein · 2007
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 hier-archically refined using EM to give accurate, compact gram-mars. The resulting grammars are extremely compact com-pared 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 addi-tion, we give an associated coarse-to-fine inference scheme which vastly improves inference time with no loss in test set accuracy.