Span Pointer Networks for Non-Autoregressive Task-Oriented Semantic Parsing

Akshat Shrivastava, Pierce Chuang, Arun Babu, Shrey Desai, Abhinav Arora, Alexander Zotov, Ahmed Aly


Abstract
An effective recipe for building seq2seq, non-autoregressive, task-oriented parsers to map utterances to semantic frames proceeds in three steps: encoding an utterance x, predicting a frame’s length |y|, and decoding a |y|-sized frame with utterance and ontology tokens. Though empirically strong, these models are typically bottlenecked by length prediction, as even small inaccuracies change the syntactic and semantic characteristics of resulting frames. In our work, we propose span pointer networks, non-autoregressive parsers which shift the decoding task from text generation to span prediction; that is, when imputing utterance spans into frame slots, our model produces endpoints (e.g., [i, j]) as opposed to text (e.g., “6pm”). This natural quantization of the output space reduces the variability of gold frames, therefore improving length prediction and, ultimately, exact match. Furthermore, length prediction is now responsible for frame syntax and the decoder is responsible for frame semantics, resulting in a coarse-to-fine model. We evaluate our approach on several task-oriented semantic parsing datasets. Notably, we bridge the quality gap between non-autogressive and autoregressive parsers, achieving 87 EM on TOPv2 (Chen et al. 2020). Furthermore, due to our more consistent gold frames, we show strong improvements in model generalization in both cross-domain and cross-lingual transfer in low-resource settings. Finally, due to our diminished output vocabulary, we observe 70% reduction in latency and 83% reduction in memory at beam size 5 compared to prior non-autoregressive parsers.
Anthology ID:
2021.findings-emnlp.161
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2021
Month:
November
Year:
2021
Address:
Punta Cana, Dominican Republic
Venues:
EMNLP | Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
1873–1886
Language:
URL:
https://aclanthology.org/2021.findings-emnlp.161
DOI:
10.18653/v1/2021.findings-emnlp.161
Bibkey:
Cite (ACL):
Akshat Shrivastava, Pierce Chuang, Arun Babu, Shrey Desai, Abhinav Arora, Alexander Zotov, and Ahmed Aly. 2021. Span Pointer Networks for Non-Autoregressive Task-Oriented Semantic Parsing. In Findings of the Association for Computational Linguistics: EMNLP 2021, pages 1873–1886, Punta Cana, Dominican Republic. Association for Computational Linguistics.
Cite (Informal):
Span Pointer Networks for Non-Autoregressive Task-Oriented Semantic Parsing (Shrivastava et al., Findings 2021)
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PDF:
https://aclanthology.org/2021.findings-emnlp.161.pdf