Unbiased and Efficient Sampling of Dependency Trees

Miloš Stanojević


Abstract
Most computational models of dependency syntax consist of distributions over spanning trees. However, the majority of dependency treebanks require that every valid dependency tree has a single edge coming out of the ROOT node, a constraint that is not part of the definition of spanning trees. For this reason all standard inference algorithms for spanning trees are sub-optimal for inference over dependency trees.Zmigrod et al (2021) proposed algorithms for sampling with and without replacement from the dependency tree distribution that incorporate the single-root constraint. In this paper we show that their fastest algorithm for sampling with replacement, Wilson-RC, is in fact producing biased samples and we provide two alternatives that are unbiased. Additionally, we propose two algorithms (one incremental, one parallel) that reduce the asymptotic runtime of algorithm for sampling k trees without replacement to O(kn^3). These algorithms are both asymptotically and practically more efficient.
Anthology ID:
2022.emnlp-main.110
Volume:
Proceedings of the 2022 Conference on Empirical Methods in Natural Language Processing
Month:
December
Year:
2022
Address:
Abu Dhabi, United Arab Emirates
Editors:
Yoav Goldberg, Zornitsa Kozareva, Yue Zhang
Venue:
EMNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
1691–1706
Language:
URL:
https://aclanthology.org/2022.emnlp-main.110
DOI:
10.18653/v1/2022.emnlp-main.110
Bibkey:
Cite (ACL):
Miloš Stanojević. 2022. Unbiased and Efficient Sampling of Dependency Trees. In Proceedings of the 2022 Conference on Empirical Methods in Natural Language Processing, pages 1691–1706, Abu Dhabi, United Arab Emirates. Association for Computational Linguistics.
Cite (Informal):
Unbiased and Efficient Sampling of Dependency Trees (Stanojević, EMNLP 2022)
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PDF:
https://aclanthology.org/2022.emnlp-main.110.pdf