Fusion-in-decoder (Fid) (Izacard and Grave, 2020) is a generative question answering (QA) model that leverages passage retrieval with a pre-trained transformer and pushed the state of the art on single-hop QA. However, the complexity of multi-hop QA hinders the effectiveness of the generative QA approach. In this work, we propose a simple generative approach (PathFid) that extends the task beyond just answer generation by explicitly modeling the reasoning process to resolve the answer for multi-hop questions. By linearizing the hierarchical reasoning path of supporting passages, their key sentences, and finally the factoid answer, we cast the problem as a single sequence prediction task. To facilitate complex reasoning with multiple clues, we further extend the unified flat representation of multiple input documents by encoding cross-passage interactions. Our extensive experiments demonstrate that PathFid leads to strong performance gains on two multi-hop QA datasets: HotpotQA and IIRC. Besides the performance gains, PathFid is more interpretable, which in turn yields answers that are more faithfully grounded to the supporting passages and facts compared to the baseline Fid model.

本文提出了一种简单而具有解释性的生成方法(PathFid)，通过显式建模推理过程来解决多跳问题的答案生成。通过线性化支持段落、关键句子和事实答案的分层推理路径，将问题作为单一序列预测任务，并编码跨段落互动以促进复杂推理。实验证明，PathFid在HotpotQA和IIRC两个多跳QA数据集上均具有很强的表现优势，并且结果更接近支持文本和事实。

将多跳问题回答建模为单序列预测