Dynamic Attention Aggregation with BERT for Neural Machine Translation

The recently proposed BERT has demonstrated great power in various natural language processing tasks. However, the model does not perform effectively on cross-lingual tasks, especially on machine translation. In this work, we propose three methods to introduce pre-trained BERT into neural machine translation without fine-tuning. Our approach consists of a) a linear-attention aggregation that leverages a parameter matrix to capture the key knowledge of BERT, b) a self-attention aggregation which aims to learn what is vital for input and output, and c) a switch-gate aggregation to dynamically control the balance of the information flowing from the pre-trained BERT or the NMT model. We conduct experiments on several translation benchmarks and substantially improve over 2 BELU points on the IWSLT'14 English - German task with switch-gate aggregation method compared to a strong baseline, while our proposed model also performs remarkably on the other tasks.