CVAE-based Re-anchoring for Implicit Discourse Relation Classification
Summary
Implicit discourse relation classification asks a model to label how two arguments relate when no connective signals it. Annotated data for this task is scarce. The authors place a VAE between a RoBERTa encoder and an MLP classifier. The VAE resamples latent variants of the argument-pair representation in every epoch, which should act as data augmentation. In practice, this setup performed worse than plain RoBERTa+MLP. The authors trace the drop to erroneous sampling: the VAE's sampling region can cross class boundaries, so some variants receive the wrong relation label.
To fix this, they use a Conditional VAE during training. It shifts the anchor of the sampling region toward a relation-type embedding, and an added risk term penalises variants that land nearer to other relations. Because gold labels are unavailable at test time, RoBERTa is trained to absorb this re-anchoring, and inference uses an ordinary VAE.
On PDTB v2.0, re-anchoring beats the RoBERTa baseline on every main relation class. Combined with transfer learning and interactive attention, the model achieves state-of-the-art 4-way results. This shows that augmentation from generative models must account for label-preserving sampling.
Key points
- Data split: PDTB v2.0, with sections 02–20 for training, 00–01 for development and 21–22 for testing. Performance is reported as binary F1 for Comparison, Contingency, Expansion and Temporal, plus 4-way F1 and accuracy.
- Plain VAE hurts: adding a VAE lowered binary F1 on all four classes. For example, Comparison fell from 53.71 to 48.22 and Expansion from 75.90 to 70.07.
- Re-anchoring helps: CVAE re-anchoring raised the scores to 56.60 (COM), 62.60 (CON), 77.74 (EXP) and 37.13 (TEM). This roughly matches transfer learning, which relies on 18,459 external explicit argument pairs.
- Risk term: the risk loss combines mean-square divergences to the true and to competing relation embeddings, weighted by α = β = 0.5. It is added to the cross-entropy loss and back-propagated into RoBERTa.
- Full model results: the full model (re-anchoring + transfer learning + interactive attention) reaches 65.06 4-way F1 and 70.17 accuracy. This exceeds Liu et al. (2020), who reported 63.39 and 69.06.
Cited by
- DiscoPrompt: Path Prediction Prompt Tuning for Implicit Discourse Relation Recognition
- Facilitating Contrastive Learning of Discourse Relational Senses by Exploiting the Hierarchy of Sense Relations
- Infusing Hierarchical Guidance into Prompt Tuning: A Parameter-Efficient Framework for Multi-level Implicit Discourse Relation Recognition
Cite
@inproceedings{dou2021cvae,
title = {{CVAE-based Re-anchoring for Implicit Discourse Relation Classification}},
author = {Dou, Zujun and Hong, Yu and Sun, Yu and Zhou, Guodong},
booktitle = {Findings of the Association for Computational Linguistics: EMNLP 2021},
year = {2021},
doi = {10.18653/v1/2021.findings-emnlp.110},
url = {https://doi.org/10.18653/v1/2021.findings-emnlp.110}
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