SentGraph: Hierarchical Sentence Graph for Multi-hop Retrieval-Augmented Question Answering

TL;DR

SentGraph introduces a hierarchical sentence graph framework that improves multi-hop question answering by explicitly modeling logical sentence relationships, leading to more accurate evidence retrieval and reasoning.

Contribution

The paper presents SentGraph, a novel sentence-level graph-based RAG framework that captures logical sentence relationships for enhanced multi-hop QA performance.

Findings

Outperforms existing methods on four multi-hop QA benchmarks.

Effectively models sentence-level logical dependencies for reasoning.

Improves evidence retrieval accuracy in multi-hop QA tasks.

Abstract

Traditional Retrieval-Augmented Generation (RAG) effectively supports single-hop question answering with large language models but faces significant limitations in multi-hop question answering tasks, which require combining evidence from multiple documents. Existing chunk-based retrieval often provides irrelevant and logically incoherent context, leading to incomplete evidence chains and incorrect reasoning during answer generation. To address these challenges, we propose SentGraph, a sentence-level graph-based RAG framework that explicitly models fine-grained logical relationships between sentences for multi-hop question answering. Specifically, we construct a hierarchical sentence graph offline by first adapting Rhetorical Structure Theory to distinguish nucleus and satellite sentences, and then organizing them into topic-level subgraphs with cross-document entity bridges. During online retrieval, SentGraph performs graph-guided evidence selection and path expansion to retrieve fine-grained sentence-level evidence. Extensive experiments on four multi-hop question answering benchmarks demonstrate the effectiveness of SentGraph, validating the importance of explicitly modeling sentence-level logical dependencies for multi-hop reasoning.