Analysing the effect of out-of-domain data on SMT systems

  • Authors:
  • Barry Haddow;Philipp Koehn

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

  • Venue:
  • WMT '12 Proceedings of the Seventh Workshop on Statistical Machine Translation
  • Year:
  • 2012

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Abstract

In statistical machine translation (SMT), it is known that performance declines when the training data is in a different domain from the test data. Nevertheless, it is frequently necessary to supplement scarce in-domain training data with out-of-domain data. In this paper, we first try to relate the effect of the out-of-domain data on translation performance to measures of corpus similarity, then we separately analyse the effect of adding the out-of-domain data at different parts of the training pipeline (alignment, phrase extraction, and phrase scoring). Through experiments in 2 domains and 8 language pairs it is shown that the out-of-domain data improves coverage and translation of rare words, but may degrade the translation quality for more common words.