Understanding the Properties of Minimum Bayes Risk Decoding in Neural Machine Translation

Mathias Müller, Rico Sennrich


Abstract
Neural Machine Translation (NMT) currently exhibits biases such as producing translations that are too short and overgenerating frequent words, and shows poor robustness to copy noise in training data or domain shift. Recent work has tied these shortcomings to beam search – the de facto standard inference algorithm in NMT – and Eikema & Aziz (2020) propose to use Minimum Bayes Risk (MBR) decoding on unbiased samples instead. In this paper, we empirically investigate the properties of MBR decoding on a number of previously reported biases and failure cases of beam search. We find that MBR still exhibits a length and token frequency bias, owing to the MT metrics used as utility functions, but that MBR also increases robustness against copy noise in the training data and domain shift.
Anthology ID:
2021.acl-long.22
Volume:
Proceedings of the 59th Annual Meeting of the Association for Computational Linguistics and the 11th International Joint Conference on Natural Language Processing (Volume 1: Long Papers)
Month:
August
Year:
2021
Address:
Online
Editors:
Chengqing Zong, Fei Xia, Wenjie Li, Roberto Navigli
Venues:
ACL | IJCNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
259–272
Language:
URL:
https://aclanthology.org/2021.acl-long.22
DOI:
10.18653/v1/2021.acl-long.22
Bibkey:
Cite (ACL):
Mathias Müller and Rico Sennrich. 2021. Understanding the Properties of Minimum Bayes Risk Decoding in Neural Machine Translation. In Proceedings of the 59th Annual Meeting of the Association for Computational Linguistics and the 11th International Joint Conference on Natural Language Processing (Volume 1: Long Papers), pages 259–272, Online. Association for Computational Linguistics.
Cite (Informal):
Understanding the Properties of Minimum Bayes Risk Decoding in Neural Machine Translation (Müller & Sennrich, ACL-IJCNLP 2021)
Copy Citation:
PDF:
https://aclanthology.org/2021.acl-long.22.pdf
Video:
 https://aclanthology.org/2021.acl-long.22.mp4
Code
 ZurichNLP/understanding-mbr