Recently, substantial progress has been made in text ranking based on pretrained language models such as BERT. However, there are limited studies on how to leverage more powerful sequence-to-sequence models such as T5. Existing attempts usually formulate text ranking as classification and rely on postprocessing to obtain a ranked list. In this paper, we propose RankT5 and study two T5-based ranking model structures, an encoder-decoder and an encoder-only one, so that they not only can directly output ranking scores for each query-document pair, but also can be fine-tuned with "pairwise" or "listwise" ranking losses to optimize ranking performances. Our experiments show that the proposed models with ranking losses can achieve substantial ranking performance gains on different public text ranking data sets. Moreover, when fine-tuned with listwise ranking losses, the ranking model appears to have better zero-shot ranking performance on out-of-domain data sets compared to the model fine-tuned with classification losses.

本文提出RankT5，通过两种基于T5的排名模型结构来直接输出每个查询文档对的排名分数，并通过'成对'或'列表'排列损失进行微调以优化排名表现。实验表明，利用排名损失的所提出的模型可以在不同的公共文本排名数据集上取得实质性的排名表现提高，并且当与分类损失精细调整后，模型在域外数据集上出现更好的零售排名表现。

RankT5：使用排序损失对T5进行文本排序微调