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Text Modular Networks: Learning to Decompose Tasks in the Language of Existing Models

Paper · 2021 · Tushar Khot, Daniel Khashabi, Kyle Richardson et al.

Summary

Text Modular Networks (TMNs) tackle complex question answering by breaking a hard question into a chain of simpler questions that existing models can already answer. Earlier decomposition methods were built for one dataset and produced sub-questions without regard to which solver would receive them. TMNs instead learn how each existing sub-model "speaks." A BART model is trained on a sub-model's own dataset, such as SQuAD, to generate questions from a context, an answer and vocabulary hints. Using distant supervision and no annotated decompositions, the authors then build step-by-step decomposition examples and train a next-question generator. This generator picks a sub-model and writes the next sub-question until it emits an end symbol. The resulting system, MODULARQA, combines a neural single-span QA model with a symbolic calculator. It covers five reasoning types: composition, conjunction, comparison, difference and complementation. It is the first decomposition-based interpretable system that works on both DROP and HotpotQA. It comes close to black-box models in accuracy while being more robust and sample-efficient, and its explanations are faithful and written in natural language.

Key points

  • On DROP, MODULARQA scores only 3.7% F1 below the black-box NumNet+V2. With 20% of the training data it outperforms NumNet+V2 (87.0 vs 85.4 F1), although NumNet+V2 leads at 100% (91.6 vs 87.8).
  • Evaluated on 239 in-scope questions from the contrast set for DROP introduced by Gardner et al. (2020), MODULARQA reaches 55.7 EM and 63.3 F1, compared with 45.2 EM and 56.2 F1 for NumNet+V2.
  • It clearly beats the DROP-specific NMN-D and roughly matches S-NMN on HotpotQA. It trails DecompRC and Quark on HotpotQA, and the authors note that both rely on dataset-specific design or supporting-fact annotations.
  • Human judges rated its explanations as more trustworthy, understandable and preferable than those of the split-based DecompRC in 67%–78% of cases.
  • Error analysis:
    • On HotpotQA, 65% of errors come from intermediate questions that have multiple or yes/no answers.
    • On DROP, errors stem mainly from decomposition (53.3%) and the QA sub-models (33.33%).
    • Code is available at github.com/allenai/modularqa.

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

 Institutions

Cite

Cite as Tushar Khot, Daniel Khashabi, Kyle Richardson, Peter Clark and Ashish Sabharwal. 2021. Text Modular Networks: Learning to Decompose Tasks in the Language of Existing Models. Proceedings of the 2021 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/2021.naacl-main.99

@inproceedings{khot2021text,
  title = {{Text Modular Networks: Learning to Decompose Tasks in the Language of Existing Models}},
  author = {Tushar Khot, Daniel Khashabi, Kyle Richardson, Peter Clark and Ashish Sabharwal},
  booktitle = {Proceedings of the 2021 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies},
  year = {2021},
  doi = {10.18653/v1/2021.naacl-main.99},
  url = {https://doi.org/10.18653/v1/2021.naacl-main.99}
}

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