Chinese Event Coreference Resolution: An Unsupervised Probabilistic Model Rivaling Supervised Resolvers
Summary
Resolving which event mentions in a document describe the same real-world happening is hard. It is even harder for Chinese, which has received little research attention and lacks large lexical resources comparable to WordNet or FrameNet, which have helped English systems. Chen and Ng address within-document Chinese event coreference in the ACE 2005 setting without any training data labeled with coreference links. They design a generative probabilistic model whose parameters are estimated with EM on raw text, treating the true antecedent as a hidden variable. The model scores candidate antecedents using trigger-word pairs and context features, which are assumed conditionally independent. It also decides jointly whether a mention is anaphoric at all, through a dummy antecedent. This matters because only about a quarter of event mentions corefer with an earlier one. On the Chinese portion of ACE 2005, the unsupervised system significantly outperforms SinoCoreferencer, a state-of-the-art supervised resolver. Because the method is language-independent and needs no knowledge bases, it could transfer to low-resource languages.
Key points
- Data and setting: The model is evaluated on the Chinese part of the ACE 2005 corpus. ACE 2005 defines 8 event types and 33 subtypes, and only 24.4% of Chinese event mentions in it are anaphoric.
- Method: The generative model estimates P(e, k, c, l), with antecedent correctness l treated as latent and learned via EM. Non-anaphoric mentions are handled by linking them to a dummy candidate antecedent.
- Main evidence of coreference: The model relies on trigger similarity, specifically BV matches and word2vec similarity. A candidate link is blocked when non-coreference conditions hold.
- Comparison with SinoCoreferencer: On 323 mentions where the two systems disagree, the unsupervised model is correct in 205 cases and SinoCoreferencer in 118. The unsupervised model is especially better at leaving singletons and non-event mentions unresolved, which explains its higher precision.
- Remaining errors: Most errors come from upstream pipeline components, including trigger and argument extraction and entity coreference, as well as from unmodeled attributes such as Modality, Polarity, Genericity, Tense and timing. The authors propose joint inference across these components as future work.
Cited by
Cite
@inproceedings{chen2015chinese,
title = {{Chinese Event Coreference Resolution: An Unsupervised Probabilistic Model Rivaling Supervised Resolvers}},
author = {Chen, Chen and Ng, Vincent},
booktitle = {Proceedings of the 2015 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies},
year = {2015},
doi = {10.3115/v1/n15-1116},
url = {https://doi.org/10.3115/v1/n15-1116}
}References
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