Gated Self-Matching Networks for Reading Comprehension and Question Answering
Summary
The paper addresses extractive reading comprehension on SQuAD, where a system must answer a question by selecting a contiguous span of a given passage. Such answers are often longer phrases, not single entities. The authors propose gated self-matching networks, an end-to-end model with four stages:
- Bi-directional GRU encoders for the question and the passage, using word and character embeddings.
- A gated attention-based recurrent layer that fuses question information into each passage word and filters it by relevance.
- A self-matching layer in which the passage attends over itself, so each word can gather evidence from distant parts of the text.
- A pointer network that predicts where the answer starts and ends.
On the hidden SQuAD test set, a single model reaches 71.3% exact match and an ensemble reaches 75.9%. Both held first place on the SQuAD leaderboard when the paper was submitted. The work matters because it shows that relevance gating combined with passage-wide self-attention addresses the limited memory of recurrent encoders in span-based QA.
Key points
- Evaluated on SQuAD (Rajpurkar et al., 2016): 71.3% exact match for the single model and 75.9% for the ensemble on the hidden test set. Both ranked first on the leaderboard at submission time (Feb. 6, 2017).
- The approach builds on match-LSTM and pointer networks (Wang and Jiang, 2016b). Its novelty is an additional sigmoid gate on the RNN input, which is the passage word concatenated with its attention-pooled question vector.
- GRU was chosen over LSTM because it performs similarly at lower computational cost. The authors report that the extra gate helps with both cell types.
- Character-level embeddings come from the final hidden states of a bi-directional RNN run over a token's characters, which helps with OOV words.
- Training minimizes the summed negative log probabilities of the gold start and end positions. MS MARCO is named as the next target dataset.
Interesting ideas
- I1. Relevance gate on attention input: a learned sigmoid gate over the concatenation of a token and its attended context can down-weight irrelevant tokens before recurrence. This filtering idea could carry over to any cross-sequence matching task, such as entailment or retrieval-based QA.
- I2. Self-matching after cross-matching: the authors first make the passage question-aware and then let it attend to itself. This lets the model use clues far from a candidate answer, which is useful wherever RNN context is too short, such as long documents or multi-sentence evidence.
- I3. Question-summary initial state for the pointer: initializing the pointer network with an attention-pooled question vector, built with a trainable query parameter, conditions span prediction on the question. This is a cheap trick for any boundary or span extraction decoder.
- I4. Character-level RNN embeddings next to word vectors: combining the two gives robustness to rare and unseen words. This could be especially helpful for morphologically rich languages such as Ukrainian.
- I5. Ablating a component across cell types: testing the added gate on both GRU and LSTM shows the gain is not tied to one architecture. This is a good evaluation habit for any proposed module.
Cited by
- Simple and Effective Multi-Paragraph Reading Comprehension
- A Span-Extraction Dataset for Chinese Machine Reading Comprehension
- DuReader: a Chinese Machine Reading Comprehension Dataset from Real-world Applications
- The NarrativeQA Reading Comprehension Challenge
- Event Extraction as Multi-turn Question Answering
- Reasoning Over Paragraph Effects in Situations
- Learned in Translation: Contextualized Word Vectors
- The Natural Language Decathlon: Multitask Learning as Question Answering
- Towards Exploiting Background Knowledge for Building Conversation Systems
- Know What You Don't Know: Unanswerable Questions for SQuAD
- Multi-passage BERT: A Globally Normalized BERT Model for Open-domain Question Answering
- K-Adapter: Infusing Knowledge into Pre-Trained Models with Adapters
- HotpotQA: A Dataset for Diverse, Explainable Multi-hop Question Answering
- QANet: Combining Local Convolution with Global Self-Attention for Reading Comprehension
- Paragraph-level Neural Question Generation with Maxout Pointer and Gated Self-attention Networks
Cite
@inproceedings{wang2017gated,
title = {{Gated Self-Matching Networks for Reading Comprehension and Question Answering}},
author = {Wang, Wenhui and Yang, Nan and Wei, Furu and Chang, Baobao and Zhou, Ming},
booktitle = {Proceedings of the 55th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)},
year = {2017},
doi = {10.18653/v1/p17-1018},
url = {https://doi.org/10.18653/v1/p17-1018}
}References
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