Abstract
Constituency parsing and nested named entity recognition (NER) are similar tasks since they both aim to predict a collection of nested and non-crossing spans. In this work, we cast nested NER to constituency parsing and propose a novel pointing mechanism for bottom-up parsing to tackle both tasks. The key idea is based on the observation that if we traverse a constituency tree in post-order, i.e., visiting a parent after its children, then two consecutively visited spans would share a boundary. Our model tracks the shared boundaries and predicts the next boundary at each step by leveraging a pointer network. As a result, it needs only linear steps to parse and thus is efficient. It also maintains a parsing configuration for structural consistency, i.e., always outputting valid trees. Experimentally, our model achieves the state-of-the-art performance on PTB among all BERT-based models (96.01 F1 score) and competitive performance on CTB7 in constituency parsing; and it also achieves strong performance on three benchmark datasets of nested NER: ACE2004, ACE2005, and GENIA. Our code will be available at https://github.com/xxxxx.- Anthology ID:
- 2022.acl-long.171
- Volume:
- Proceedings of the 60th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
- Month:
- May
- Year:
- 2022
- Address:
- Dublin, Ireland
- Venue:
- ACL
- SIG:
- Publisher:
- Association for Computational Linguistics
- Note:
- Pages:
- 2403–2416
- Language:
- URL:
- https://aclanthology.org/2022.acl-long.171
- DOI:
- 10.18653/v1/2022.acl-long.171
- Cite (ACL):
- Songlin Yang and Kewei Tu. 2022. Bottom-Up Constituency Parsing and Nested Named Entity Recognition with Pointer Networks. In Proceedings of the 60th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers), pages 2403–2416, Dublin, Ireland. Association for Computational Linguistics.
- Cite (Informal):
- Bottom-Up Constituency Parsing and Nested Named Entity Recognition with Pointer Networks (Yang & Tu, ACL 2022)
- PDF:
- https://preview.aclanthology.org/nodalida-main-page/2022.acl-long.171.pdf
- Code
- sustcsonglin/pointer-net-for-nested
- Data
- GENIA, Penn Treebank