An Empirical Study of Iterative Refinements for Non-autoregressive Translation

Iterative non-autoregressive (NAR) models share a spirit of mixed autoregressive (AR) and fully NAR models, seeking a balance between generation quality and inference efficiency. These models have recently demonstrated impressive performance in varied generation tasks, surpassing the autoregressive Transformer. However, they also face several challenges that impede further development. In this work, we target building more efficient and competitive iterative NAR models. Firstly, we produce two simple metrics to identify the potential problems existing in current refinement processes, and look back on the various iterative NAR models to find the key factors for realizing our purpose. Subsequently, based on the analyses of the limitations of previous inference algorithms, we propose a simple yet effective strategy to conduct efficient refinements without performance declines. Experiments on five widely used datasets show that our final models set the new state-of-the-art performance compared to all previous NAR models, even with fewer decoding steps, and outperform AR Transformer by around one BLEU on average. Our codes and models are available on Github.