N-best reranking by multitask learning

  • Authors:
  • Kevin Duh;Katsuhito Sudoh;Hajime Tsukada;Hideki Isozaki;Masaaki Nagata

  • Affiliations:
  • NTT Communication Science Laboratories, Soraku-gun, Kyoto, Japan;NTT Communication Science Laboratories, Soraku-gun, Kyoto, Japan;NTT Communication Science Laboratories, Soraku-gun, Kyoto, Japan;NTT Communication Science Laboratories, Soraku-gun, Kyoto, Japan;NTT Communication Science Laboratories, Soraku-gun, Kyoto, Japan

  • Venue:
  • WMT '10 Proceedings of the Joint Fifth Workshop on Statistical Machine Translation and MetricsMATR
  • Year:
  • 2010

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Abstract

We propose a new framework for N-best reranking on sparse feature sets. The idea is to reformulate the reranking problem as a Multitask Learning problem, where each N-best list corresponds to a distinct task. This is motivated by the observation that N-best lists often show significant differences in feature distributions. Training a single reranker directly on this heteroge-nous data can be difficult. Our proposed meta-algorithm solves this challenge by using multitask learning (such as ℓ1/ℓ2 regularization) to discover common feature representations across N-best lists. This meta-algorithm is simple to implement, and its modular approach allows one to plug-in different learning algorithms from existing literature. As a proof of concept, we show statistically significant improvements on a machine translation system involving millions of features.