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Leveraging Passage Retrieval with Generative Models for Open Domain Question Answering

Written for the Research library (claude-opus-5-5) from the paper text. Original — aclanthology.org/2021.eacl-main.74.pdf

Summary

Open-domain question answering means answering factual questions when the system is not given the text that contains the answer. A closed-book generative approach (T5) stores all its knowledge in model weights, so it needs billions of parameters and is costly to train and run. This paper pairs retrieval with a generative reader. First, BM25 or DPR fetches supporting Wikipedia passages. Then a pretrained T5 model reads them. The encoder handles each passage separately, together with its title and the question. The decoder attends over the joined encodings of all passages, a design the authors call Fusion-in-Decoder. Because the encoder looks at one passage at a time, cost grows linearly with the number of passages, so the reader can take in 100 of them. The authors scored the model with exact match on open versions of NaturalQuestions, TriviaQA and SQuAD v1.1. It got the best published scores on the first two, and accuracy kept rising as more passages were added. This suggests that generative readers are good at combining evidence spread across many documents.

Key points

  • Architecture: Fusion-in-Decoder is built on T5 base (220M parameters) and T5 large (770M). Its inputs are tagged with the special tokens question:, title: and context:. The model reads 100 retrieved passages, each cut to 250 word pieces. DPR is the retriever for NQ and TriviaQA, and BM25 is used for SQuAD.
  • Large model, exact match: 51.4 on NaturalQuestions, 67.6 on open TriviaQA (80.1 on the hidden test set) and 56.7 on SQuAD Open (F1 63.2). These scores beat REALM, DPR, RAG, SpanSeqGen and GPT-3 few-shot.
  • Retrieval vs. size: With 770M parameters plus BM25 retrieval over Wikipedia, the model reaches 44.1% on NQ. The 11B closed-book T5 scores 36.6%, while storing roughly the same amount of information.
  • More passages help: Going from 10 to 100 retrieved passages adds about 6 points on TriviaQA and 3.5 on NQ. Extractive readers usually stop improving at around 10–20 passages.
  • Setup: Wikipedia dumps from December 2018 (NQ, TriviaQA) and December 2016 (SQuAD) were split into non-overlapping 100-word passages. Training used 64 V100 GPUs for 10k steps with batch size 64.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

Fields: Natural language processing

Cited by

647 papers of our library cite it (of the 140673 whose bibliographies we read); 42 of them have a page here, 605 not yet.

Cite

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/2021.eacl-main.74 · arXiv 2007.01282

@inproceedings{izacard2021leveraging,
  title = {{Leveraging Passage Retrieval with Generative Models for Open Domain Question Answering}},
  author = {Izacard, Gautier and Grave, Edouard},
  booktitle = {Proceedings of the 16th Conference of the European Chapter of the Association for Computational Linguistics: Main Volume},
  year = {2021},
  doi = {10.18653/v1/2021.eacl-main.74},
  eprint = {2007.01282},
  archivePrefix = {arXiv},
  url = {https://doi.org/10.18653/v1/2021.eacl-main.74}
}

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