Towards Making the Most of BERT in Neural Machine Translation

TL;DR

This paper introduces CTNMT, a training framework that effectively integrates pre-trained language models like BERT into neural machine translation, improving translation quality and surpassing previous state-of-the-art results.

Contribution

The paper proposes a novel concerted training framework with techniques to retain pre-trained knowledge and prevent catastrophic forgetting in NMT models.

Findings

Up to 3 BLEU score improvement on WMT14 English-German

Surpasses previous state-of-the-art pre-training aided NMT by 1.4 BLEU

Significant improvements on large-scale English-French translation

Abstract

GPT-2 and BERT demonstrate the effectiveness of using pre-trained language models (LMs) on various natural language processing tasks. However, LM fine-tuning often suffers from catastrophic forgetting when applied to resource-rich tasks. In this work, we introduce a concerted training framework (CTNMT) that is the key to integrate the pre-trained LMs to neural machine translation (NMT). Our proposed CTNMT consists of three techniques: a) asymptotic distillation to ensure that the NMT model can retain the previous pre-trained knowledge; b) a dynamic switching gate to avoid catastrophic forgetting of pre-trained knowledge; and c) a strategy to adjust the learning paces according to a scheduled policy. Our experiments in machine translation show CTNMT gains of up to 3 BLEU score on the WMT14 English-German language pair which even surpasses the previous state-of-the-art pre-training aided NMT by 1.4 BLEU score. While for the large WMT14 English-French task with 40 millions of sentence-pairs, our base model still significantly improves upon the state-of-the-art Transformer big model by more than 1 BLEU score. The code and model can be downloaded from https://github.com/bytedance/neurst/ tree/master/examples/ctnmt.