Retrieval-augmented generation (RAG) effectively addresses issues of static knowledge and hallucination in large language models. Existing studies mostly focus on question scenarios with clear user intents and concise answers. However, it is prevalent that users issue broad, open-ended queries with diverse sub-intents, for which they desire rich and long-form answers covering multiple relevant aspects. To tackle this important yet underexplored problem, we propose a novel RAG framework, namely RichRAG. It includes a sub-aspect explorer to identify potential sub-aspects of input questions, a multi-faceted retriever to build a candidate pool of diverse external documents related to these sub-aspects, and a generative list-wise ranker, which is a key module to provide the top-k most valuable documents for the final generator. These ranked documents sufficiently cover various query aspects and are aware of the generator's preferences, hence incentivizing it to produce rich and comprehensive responses for users. The training of our ranker involves a supervised fine-tuning stage to ensure the basic coverage of documents, and a reinforcement learning stage to align downstream LLM's preferences to the ranking of documents. Experimental results on two publicly available datasets prove that our framework effectively and efficiently provides comprehensive and satisfying responses to users.

为了解决用户在发出宽泛、开放式的查询时得到丰富的、多方面的回复的问题，我们提出了一种新颖的检索增强生成框架——RichRAG。该框架包括一个子方面探索器，用于识别问题中的潜在子方面；一个多方面检索器，用于构建与这些子方面相关的多样化外部文档的候选池；以及一个生成型列表排序器，它是为最终生成器提供前k个最有价值的文档的关键模块。经过实验证明，我们的框架能够有效、高效地为用户提供全面且满意的回复。

RichRAG：在检索增强生成中为多方面查询创建丰富的回复