Back translation is one of the most widely used methods for improving the performance of neural machine translation systems. Recent research has sought to enhance the effectiveness of this method by increasing the 'diversity' of the generated translations. We argue that the definitions and metrics used to quantify 'diversity' in previous work have been insufficient. This work puts forward a more nuanced framework for understanding diversity in training data, splitting it into lexical diversity and syntactic diversity. We present novel metrics for measuring these different aspects of diversity and carry out empirical analysis into the effect of these types of diversity on final neural machine translation model performance for low-resource English$\leftrightarrow$Turkish and mid-resource English$\leftrightarrow$Icelandic. Our findings show that generating back translation using nucleus sampling results in higher final model performance, and that this method of generation has high levels of both lexical and syntactic diversity. We also find evidence that lexical diversity is more important than syntactic for back translation performance.

本研究提出比以往更细致的“多样性”框架，将其分为词汇和句法多样性，并针对低资源和中资源机器翻译任务，提出创新的度量标准用于衡量这些不同方面的多样性。实证分析表明，使用核采样生成反向翻译能够提高最终模型性能，并且这种生成方法具有很高的词汇和句法多样性。研究还发现证据表明词汇多样性比句法多样性更重要。

低资源机器翻译中的后向翻译多样性探究