Title: Top-Rank Enhanced Listwise Optimization for Statistical Machine Translation,
Abstract: Pairwise ranking methods are the basis of many widely used discriminative
training approaches for structure prediction problems in natural language
processing(NLP). Decomposing the problem of ranking hypotheses into pairwise
comparisons enables simple and efficient solutions. However, neglecting the
global ordering of the hypothesis list may hinder learning. We propose a
listwise learning framework for structure prediction problems such as machine
translation. Our framework directly models the entire translation list's
ordering to learn parameters which may better fit the given listwise samples.
Furthermore, we propose top-rank enhanced loss functions, which are more
sensitive to ranking errors at higher positions. Experiments on a large-scale
Chinese-English translation task show that both our listwise learning framework
and top-rank enhanced listwise losses lead to significant improvements in
translation quality.