Optimization in Coreference Resolution is not Needed: A Nearly-Optimal Algorithm with Intensional Constraints
Summary
The paper tackles a practical obstacle to using Zero-One Integer Linear Programming (ILP) for coreference resolution. Global constraints such as transitivity, together with exclusivity rules derived from binding, are needed to make the decisions of a pairwise classifier consistent. However, standard ILP requires every instance of these constraints to be written out in advance, which quickly becomes intractable. The authors adapt the Balas (1965) algorithm so that constraints are handled intensionally, meaning instances are generated only when the search actually needs them. Weights come from a TiMBL memory-based pairwise classifier, converted into classification costs. Experiments on German use the TüBa-D/Z coreference corpus with five-fold cross-validation. The central finding is that the first consistent solution found by the search (Balas-First) is as good as the fully optimized one in F-measure, and even marginally better. This matters because exhaustive NP-complete optimization can be skipped, which often cuts runtime substantially. Global consistency still significantly improves on the raw classifier output, and the Balas weight ordering beats a linear ordering.
Key points
- Data. TüBa-D/Z is a treebank of 1,100 German newspaper texts and about 25,000 sentences. It contains 13,818 anaphoric, 1,031 cataphoric and 12,752 coreferential relations.
- Candidate pairs and features. The TiMBL classifier uses features such as distance, POS, grammatical function, head match, salience and semantic class. Candidate pairs are generated only within a 3-sentence sliding window.
- Why intensional constraints are needed. Writing out transitivity for about 150 noun phrases (roughly 30 sentences) already yields around 1,500,000 equations.
- Approximating c-command. Exclusivity relies on simple predicates (clause bound, np bound) instead of full syntactic c-command.
- Ordering results.
- With all mentions, F rises from 62.83 to 64.27 (+1.44) when Balas ordering replaces linear ordering.
- With true mentions, F rises from 76.08 to 78.90 (+2.82).
- Without boundness enforcement constraints, solving takes quadratic time.
Cited by
- Extending BART to Provide a Coreference Resolution System for German
- Bootstrapping coreference resolution using word associations
- Supervised Noun Phrase Coreference Research: The First Fifteen Years
- A Global Relaxation Labeling Approach to Coreference Resolution
Cite
@inproceedings{klenner2009optimization,
title = {{Optimization in Coreference Resolution is not Needed: A Nearly-Optimal Algorithm with Intensional Constraints}},
author = {Klenner, Manfred and Ailloud, Étienne},
booktitle = {Proceedings of the 12th Conference of the European Chapter of the ACL (EACL 2009)},
year = {2009},
url = {https://aclanthology.org/E09-1051/}
}References
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