Simulating morphological analyzers with stochastic taggers for confidence estimation

  • Authors:
  • Christian Monson;Kristy Hollingshead;Brian Roark

  • Affiliations:
  • Center for Spoken Language Understanding, Oregon Health & Science University;Center for Spoken Language Understanding, Oregon Health & Science University;Center for Spoken Language Understanding, Oregon Health & Science University

  • Venue:
  • CLEF'09 Proceedings of the 10th cross-language evaluation forum conference on Multilingual information access evaluation: text retrieval experiments
  • Year:
  • 2009

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Abstract

We propose a method for providing stochastic confidence estimates for rule-based and black-box natural language (NL) processing systems. Our method does not require labeled training data: We simply train stochastic models on the output of the original NL systems. Numeric confidence estimates enable both minimum Bayes risk-style optimization as well as principled system combination for these knowledge-based and black-box systems. In our specific experiments, we enrich ParaMor, a rule-based system for unsupervised morphology induction, with probabilistic segmentation confidences by training a statistical natural language tagger to simulate ParaMor's morphological segmentations. By adjusting the numeric threshold above which the simulator proposes morpheme boundaries, we improve F1 of morpheme identification on a Hungarian corpus by 5.9% absolute. With numeric confidences in hand, we also combine ParaMor's segmentation decisions with those of a second (blackbox) unsupervised morphology induction system, Morfessor. Our joint ParaMor-Morfessor system enhances F1 performance by a further 3.4% absolute, ultimately moving F1 from 41.4% to 50.7%.