Combining constituent parsers

  • Authors:
  • Victoria Fossum;Kevin Knight

  • Affiliations:
  • University of Michigan, Ann Arbor, MI;University of Southern California, Marina del Rey, CA

  • Venue:
  • NAACL-Short '09 Proceedings of Human Language Technologies: The 2009 Annual Conference of the North American Chapter of the Association for Computational Linguistics, Companion Volume: Short Papers
  • Year:
  • 2009

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Abstract

Combining the 1-best output of multiple parsers via parse selection or parse hybridization improves f-score over the best individual parser (Henderson and Brill, 1999; Sagae and Lavie, 2006). We propose three ways to improve upon existing methods for parser combination. First, we propose a method of parse hybridization that recombines context-free productions instead of constituents, thereby preserving the structure of the output of the individual parsers to a greater extent. Second, we propose an efficient linear-time algorithm for computing expected f-score using Minimum Bayes Risk parse selection. Third, we extend these parser combination methods from multiple 1-best outputs to multiple n-best outputs. We present results on WSJ section 23 and also on the English side of a Chinese-English parallel corpus.