Transformational priors over grammars

  • Authors:
  • Jason Eisner

  • Affiliations:
  • Johns Hopkins University, Baltimore, MD

  • Venue:
  • EMNLP '02 Proceedings of the ACL-02 conference on Empirical methods in natural language processing - Volume 10
  • Year:
  • 2002

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Abstract

This paper proposes a novel class of PCFG parameterizations that support linguistically reasonable priors over PCFGs. To estimate the parameters is to discover a notion of relatedness among context-free rules such that related rules tend to have related probabilities. The prior favors grammars in which the relationships are simple to describe and have few major exceptions. A basic version that bases relatedness on weighted edit distance yields superior smoothing of grammars learned from the Penn Treebank (20% reduction of rule perplexity over the best previous method).