Chinese Zero Pronoun Resolution with Deep Neural Networks
Summary
Chinese text often omits pronouns, leaving gaps (zero pronouns) that refer back to earlier mentions. Resolving these anaphoric zero pronouns (AZPs) is harder than resolving overt pronouns because the gaps carry no number or gender cues. The strongest earlier systems, the unsupervised CN14 and CN15 models, depend on heavy feature engineering, use no lexical information, and optimize data likelihood rather than resolution accuracy. Chen and Ng instead train a supervised, ranking-based deep network that they call an embedding matching approach. The AZP and each candidate antecedent are encoded from pretrained word embeddings combined with hand-crafted features. Each encoding passes through several tanh layers to produce a compact representation. The AZP's representation is then scored against each candidate's, and softmax converts the scores into probabilities. On the Chinese part of OntoNotes 5.0, the network surpasses CN15 and sets a new state of the art. The authors present it as the first neural approach to zero pronoun resolution. Its significance is that embeddings let the model generalize over lexical contexts that unsupervised resolvers could not exploit.
Key points
- Data and evaluation: experiments use the Chinese portion of OntoNotes 5.0 under three settings, each scored by recall, precision and F-score:
- gold parses with gold AZPs;
- gold parses with system-detected AZPs;
- system parses with system AZPs.
- Training instances: each AZP is paired with four candidates. One is the closest correct antecedent, and the other three are the most salient non-coreferent entities. Salience weights a mention's grammatical role (subject 4, object 2, other 1) and decays by 0.5 per sentence of distance. Only entities mentioned within two sentences of the AZP are considered.
- Full-system F-scores: 52.2 in Setting 1, 32.1 in Setting 2 and 18.4 in Setting 3.
- Ablation: using only embedding features drops Setting 1 to 40.0 F, and using only hand-crafted features gives 48.5 F. The two feature types therefore complement each other. During training, F-score levels off near 52% around epoch 80, which the authors take as evidence that the ranking objective tracks the evaluation metric.
- Error analysis: the lexical context is narrow, covering only the word before the AZP, its governing verb and the candidate's head word. Most errors stem from this limited context. The authors suggest matching sentence embeddings of the surrounding clauses as future work.
Cited by
- Tackling Zero Pronoun Resolution and Non-Zero Coreference Resolution Jointly
- Neural Japanese Zero Anaphora Resolution using Smoothed Large-scale Case Frames with Word Embedding
- An Empirical Study of Contextual Data Augmentation for Japanese Zero Anaphora Resolution
- Generating and Exploiting Large-scale Pseudo Training Data for Zero Pronoun Resolution
- Entity-Centric Joint Modeling of Japanese Coreference Resolution and Predicate Argument Structure Analysis
- ZPR2: Joint Zero Pronoun Recovery and Resolution using Multi-Task Learning and BERT
- A Joint Model for Dropped Pronoun Recovery and Conversational Discourse Parsing in Chinese Conversational Speech
- Zero Pronoun Resolution with Attention-based Neural Network
Cite
@inproceedings{chen2016chinese,
title = {{Chinese Zero Pronoun Resolution with Deep Neural Networks}},
author = {Chen, Chen and Ng, Vincent},
booktitle = {Proceedings of the 54th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)},
year = {2016},
doi = {10.18653/v1/p16-1074},
url = {https://doi.org/10.18653/v1/p16-1074}
}References
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