Dense Passage Retrieval for Open-Domain Question Answering
Written for the Research library (claude-opus-5-5) from the paper text. Original — aclanthology.org/2020.emnlp-main.550.pdf
Summary
Open-domain question answering systems usually first pull a small set of candidate passages from a huge corpus, and then a reader model extracts the answer from them. Until this paper, that first step was dominated by sparse keyword methods such as TF-IDF and BM25. Earlier dense alternatives like ORQA needed costly extra pretraining. The authors show that this pretraining is unnecessary. Their Dense Passage Retriever (DPR) is a dual encoder: two separate BERT-base models embed questions and passages, and relevance is scored by dot product. It is trained only on existing question–passage pairs. The key training choice is to treat the gold passages of other questions in the same mini-batch as negatives, plus one hard negative per question taken from BM25. Passages from a 21-million-passage Wikipedia split are encoded ahead of time and searched with FAISS. Across several benchmarks, DPR clearly beats BM25 on retrieval. Paired with a standard reader, it sets new state-of-the-art end-to-end results. The work made dense retrieval a practical default for QA and retrieval-augmented generation.
Key points
- On top-20 passage retrieval accuracy, DPR beats a Lucene-BM25 baseline by 9–19 absolute points across open-domain QA datasets. On Natural Questions, top-5 accuracy is 65.2% for DPR vs. 42.9% for BM25.
- End-to-end exact match on open Natural Questions is 41.5%, compared with 33.3% for ORQA. A jointly trained retriever–reader variant reached only 39.8 EM.
- Setup: two independent BERT-base (uncased) encoders, using the 768-dimensional [CLS] vector. Training uses in-batch negatives plus one BM25 hard negative. The ablations found that other similarity functions gave no meaningful gain over the dot product.
- The reader works best with about 50 retrieved passages on NQ. Using only 10 gives 40.8 EM, a small drop. Up to 100 passages still fit in one batch on a single 32GB GPU.
- Code and trained models are available at github.com/facebookresearch/DPR. DPR was later used as the retriever in generation-based systems built on BART and T5.
Cited by
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- LinkBERT: Pretraining Language Models with Document Links
- Making Retrieval-Augmented Language Models Robust to Irrelevant Context
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- BARTScore: Evaluating Generated Text as Text Generation
- MIRACL: A Multilingual Retrieval Dataset Covering 18 Diverse Languages
- Qwen3 Embedding: Advancing Text Embedding and Reranking Through Foundation Models
- Large Language Models for Information Retrieval: A Survey
- ToolQA: A Dataset for LLM Question Answering with External Tools
Cite
@inproceedings{karpukhin2020dense,
title = {{Dense Passage Retrieval for Open-Domain Question Answering}},
author = {Karpukhin, Vladimir and Oguz, Barlas and Min, Sewon and Lewis, Patrick and Wu, Ledell and Edunov, Sergey and Chen, Danqi and Yih, Wen-tau},
booktitle = {Proceedings of the 2020 Conference on Empirical Methods in Natural Language Processing (EMNLP)},
year = {2020},
doi = {10.18653/v1/2020.emnlp-main.550},
eprint = {2004.04906},
archivePrefix = {arXiv},
url = {https://doi.org/10.18653/v1/2020.emnlp-main.550}
}References
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