HF-RAG: Hierarchical Fusion-based RAG with Multiple Sources and Rankers

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Main Authors: Santra, Payel, Ghosh, Madhusudan, Ganguly, Debasis, Basuchowdhuri, Partha, Naskar, Sudip Kumar
Format: Preprint
Published: 2025
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author Santra, Payel
Ghosh, Madhusudan
Ganguly, Debasis
Basuchowdhuri, Partha
Naskar, Sudip Kumar
author_facet Santra, Payel
Ghosh, Madhusudan
Ganguly, Debasis
Basuchowdhuri, Partha
Naskar, Sudip Kumar
contents Leveraging both labeled (input-output associations) and unlabeled data (wider contextual grounding) may provide complementary benefits in retrieval augmented generation (RAG). However, effectively combining evidence from these heterogeneous sources is challenging as the respective similarity scores are not inter-comparable. Additionally, aggregating beliefs from the outputs of multiple rankers can improve the effectiveness of RAG. Our proposed method first aggregates the top-documents from a number of IR models using a standard rank fusion technique for each source (labeled and unlabeled). Next, we standardize the retrieval score distributions within each source by applying z-score transformation before merging the top-retrieved documents from the two sources. We evaluate our approach on the fact verification task, demonstrating that it consistently improves over the best-performing individual ranker or source and also shows better out-of-domain generalization.
format Preprint
id arxiv_https___arxiv_org_abs_2509_02837
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle HF-RAG: Hierarchical Fusion-based RAG with Multiple Sources and Rankers
Santra, Payel
Ghosh, Madhusudan
Ganguly, Debasis
Basuchowdhuri, Partha
Naskar, Sudip Kumar
Information Retrieval
Artificial Intelligence
Leveraging both labeled (input-output associations) and unlabeled data (wider contextual grounding) may provide complementary benefits in retrieval augmented generation (RAG). However, effectively combining evidence from these heterogeneous sources is challenging as the respective similarity scores are not inter-comparable. Additionally, aggregating beliefs from the outputs of multiple rankers can improve the effectiveness of RAG. Our proposed method first aggregates the top-documents from a number of IR models using a standard rank fusion technique for each source (labeled and unlabeled). Next, we standardize the retrieval score distributions within each source by applying z-score transformation before merging the top-retrieved documents from the two sources. We evaluate our approach on the fact verification task, demonstrating that it consistently improves over the best-performing individual ranker or source and also shows better out-of-domain generalization.
title HF-RAG: Hierarchical Fusion-based RAG with Multiple Sources and Rankers
topic Information Retrieval
Artificial Intelligence
url https://arxiv.org/abs/2509.02837