Abstract
We present a bracketing-based encoding that can be used to represent any 2-planar dependency tree over a sentence of length n as a sequence of n labels, hence providing almost total coverage of crossing arcs in sequence labeling parsing. First, we show that existing bracketing encodings for parsing as labeling can only handle a very mild extension of projective trees. Second, we overcome this limitation by taking into account the well-known property of 2-planarity, which is present in the vast majority of dependency syntactic structures in treebanks, i.e., the arcs of a dependency tree can be split into two planes such that arcs in a given plane do not cross. We take advantage of this property to design a method that balances the brackets and that encodes the arcs belonging to each of those planes, allowing for almost unrestricted non-projectivity (∼99.9% coverage) in sequence labeling parsing. The experiments show that our linearizations improve over the accuracy of the original bracketing encoding in highly non-projective treebanks (on average by 0.4 LAS), while achieving a similar speed. Also, they are especially suitable when PoS tags are not used as input parameters to the models.- Anthology ID:
- 2020.coling-main.223
- Volume:
- Proceedings of the 28th International Conference on Computational Linguistics
- Month:
- December
- Year:
- 2020
- Address:
- Barcelona, Spain (Online)
- Editors:
- Donia Scott, Nuria Bel, Chengqing Zong
- Venue:
- COLING
- SIG:
- Publisher:
- International Committee on Computational Linguistics
- Note:
- Pages:
- 2472–2484
- Language:
- URL:
- https://aclanthology.org/2020.coling-main.223
- DOI:
- 10.18653/v1/2020.coling-main.223
- Cite (ACL):
- Michalina Strzyz, David Vilares, and Carlos Gómez-Rodríguez. 2020. Bracketing Encodings for 2-Planar Dependency Parsing. In Proceedings of the 28th International Conference on Computational Linguistics, pages 2472–2484, Barcelona, Spain (Online). International Committee on Computational Linguistics.
- Cite (Informal):
- Bracketing Encodings for 2-Planar Dependency Parsing (Strzyz et al., COLING 2020)
- PDF:
- https://preview.aclanthology.org/nschneid-patch-4/2020.coling-main.223.pdf
- Code
- mstrise/dep2label