Simple semi-supervised learning for prepositional phrase attachment

  • Authors:
  • Gregory F. Coppola;Alexandra Birch;Tejaswini Deoskar;Mark Steedman

  • Affiliations:
  • University of Edinburgh, Edinburgh, UK;University of Edinburgh, Edinburgh, UK;University of Edinburgh, Edinburgh, UK;University of Edinburgh, Edinburgh, UK

  • Venue:
  • IWPT '11 Proceedings of the 12th International Conference on Parsing Technologies
  • Year:
  • 2011

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Abstract

Prepositional phrase attachment is an important subproblem of parsing, performance on which suffers from limited availability of labelled data. We present a semi-supervised approach. We show that a discriminative lexical model trained from labelled data, and a generative lexical model learned via Expectation Maximization from unlabelled data can be combined in a product model to yield a PP-attachment model which is better than either is alone, and which outperforms the modern parser of Petrov and Klein (2007) by a significant margin. We show that, when learning from unlabelled data, it can be beneficial to model the generation of modifiers of a head collectively, rather than individually. Finally, we suggest that our pair of models will be interesting to combine using new techniques for discriminatively constraining EM.