GNN-RAG: Graph Neural Retrieval for Efficient Large Language Model Reasoning on Knowledge Graphs

Retrieval-augmented generation (RAG) in Knowledge Graph Question Answering (KGQA) enhances the context of Large Language Models (LLMs) by incorporating information retrieved from the Knowledge Graph (KG). Most recent approaches rely on costly LLM calls to generate executable relation paths or traverse the KG, which is inefficient in complex KGQA tasks, such as those involving multi-hop or multi-entity questions. We introduce the GNN-RAG framework, which utilizes lightweight Graph Neural Networks (GNNs) for effective and efficient graph retrieval. The GNN learns to assign importance weights to nodes based on their relevance to the question, as well as the relevance of their neighboring nodes. This enables the framework to effectively handle context from distant nodes in the graph, improving retrieval performance. GNN-RAG retrieves the shortest paths connecting question entities to GNN answer candidates, providing this information as context for the LLM. Experimental results show that GNN-RAG achieves effective retrieval on two widely used KGQA benchmarks (WebQSP and CWQ), outperforming or matching GPT-4 performance with a 7B tuned LLM. Additionally, GNN-RAG excels on multi-hop and multi-entity questions outperforming LLM-based retrieval approaches by 8.9-15.5% points at answer F1. Furthermore, it surpasses long-context inference while using 9× fewer KG tokens. The code is provided in https://github.com/cmavro/GNN-RAG.