Multigraph Clustering for Unsupervised Coreference Resolution
Summary
This paper addresses coreference resolution, the task of grouping text mentions that point to the same entity, without any training data. Each document becomes a directed labeled weighted multigraph. Mentions are the nodes, and edges carry pairwise relations that may link a later mention to an earlier one. The relations are standard indicators taken from earlier work. Negative constraints, such as gender or number disagreement, receive a weight of −∞. Positive cues, such as string match or syntactic parallelism, each receive a weight of 1. Because no weights are learned, the model counts as unsupervised. Clustering is done greedily with a 1-nearest-neighbor strategy: each mention attaches to the earlier candidate with the most positive relations and no negative one, with ties going to the closest candidate. On the English track of the CoNLL'12 shared task, under closed-track conditions, the system beats most participating systems. It also compares favorably with supervised weighting variants. An error analysis points to ambiguous pronouns and nominals with different heads as the main weaknesses. The results suggest that simple, carefully chosen relations can rival heavily engineered or learned systems.
Key points
- The relation set has 23 binary relations: 9 negative (e.g., N_Gender, N_Number, N_Mod, N_ItDist) and 14 positive (e.g., P_AnaPron, P_Subject, P_Pron_StrMatch). Relations and their distance thresholds were tuned on development data.
- The data is the CoNLL'12 English data, a subset of OntoNotes 5.0, with the official dev/test split. Resources are limited to WordNet, Bergsma and Lin's (2006) number/gender data, and the provided annotation layers. System mentions come from the extractor of Martschat et al. (2012).
- The unsupervised model's F1 gains over the supervised weighting variants are statistically significant by paired t-test (p < 0.05). The one exception is the MUC F1 comparison against the "weights fraction" variant.
- Precision is weakest on pronouns such as it, with 64% of 1,114 decisions wrong, and on nominal–nominal pairs, at 49% wrong. Speaker relations make I and my comparatively reliable.
- The development set contains 3,528 recall errors, mostly nominal–nominal pairs. In a sample of 50 such errors, 29 stemmed from missing semantic knowledge, 14 from an overly strict N_Mod, and 4 from overly cautious string matching.
Cited by
- Unsupervised Ranking Model for Entity Coreference Resolution
- Recall Error Analysis for Coreference Resolution
Cite
@inproceedings{martschat2013multigraph,
title = {{Multigraph Clustering for Unsupervised Coreference Resolution}},
author = {Martschat, Sebastian},
booktitle = {51st Annual Meeting of the Association for Computational Linguistics Proceedings of the Student Research Workshop},
year = {2013},
url = {https://aclanthology.org/P13-3012/}
}References
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