HPSG supertagging: a sequence labeling view

  • Authors:
  • Yao-zhong Zhang;Takuya Matsuzaki;Jun'ichi Tsujii

  • Affiliations:
  • University of Tokyo;University of Tokyo;University of Tokyo and University of Manchester and National Centre for Text Mining, UK

  • Venue:
  • IWPT '09 Proceedings of the 11th International Conference on Parsing Technologies
  • Year:
  • 2009

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Abstract

Supertagging is a widely used speed-up technique for deep parsing. In another aspect, supertagging has been exploited in other NLP tasks than parsing for utilizing the rich syntactic information given by the supertags. However, the performance of supertagger is still a bottleneck for such applications. In this paper, we investigated the relationship between supertagging and parsing, not just to speed up the deep parser; We started from a sequence labeling view of HPSG supertagging, examining how well a supertagger can do when separated from parsing. Comparison of two types of supertagging model, point-wise model and sequential model, showed that the former model works competitively well despite its simplicity, which indicates the true dependency among supertag assignments is far more complex than the crude first-order approximation made in the sequential model. We then analyzed the limitation of separated supertagging by using a CFG-filter. The results showed that big gains could be acquired by resorting to a light-weight parser.