Context Tracking Network: Graph-based Context Modeling for Implicit Discourse Relation Recognition
Summary
Implicit discourse relation recognition (IDRR) asks a model to label the logical link between two neighbouring sentences when no connective such as "because" or "but" is present. Most earlier systems look only at the sentence pair. The main context-aware alternative, a hierarchical BiLSTM (H-LSTM), mixes the whole paragraph indiscriminately and handles distant dependencies poorly.
The authors propose CT-Net, which converts a paragraph into a paragraph association graph (PAG). In this graph, sentence nodes are joined by adjacency, co-reference and lexical chain edges, and each sentence node connects to its own token nodes. A cross-grained updating mechanism then runs for several rounds. Each round moves information from tokens to sentences (Sentence-state LSTM), across sentences (Multi-Relational GCN), and back to tokens.
The final context vectors for the target pair are fused with local BiLSTM encodings. The model is trained jointly with auxiliary tasks. On PDTB 2.0, CT-Net outperforms models that treat context coarsely. This suggests that selectively tracking relevant context, regardless of distance, benefits IDRR.
Key points
- Evaluation uses PDTB 2.0, which has 16,224 implicit and 18,459 explicit instances. The split follows Pitler et al. (2009): sections 2-20 for training, 0-1 for validation and 21-22 for test. Tasks are one-vs-others binary and 4-way classification over Comp., Cont., Exp. and Temp., scored by F1 (macro-F1 for 4-way).
- Each PAG covers 6 sentences, with zero padding for shorter texts. Co-reference chains come from spaCy, and synonyms come from WordNet. A PAG has about 11 edges on average.
- WordNet-based links cover only about 57–59% of samples in each split.
- Token nodes start from concatenated char, GloVe and ELMo embeddings. Sentence nodes start as the average of their tokens.
- Training is multi-task: IDRR is the main objective, supported by two auxiliary objectives, classifying relations that have an overt connective (explicit discourse relation recognition, EDRR) and predicting the connective itself (CP). All three share one encoder but use separate MLPs. The code is public on GitHub (yxuezhang/CTNet).
Cited by
- Where Are We in Discourse Relation Recognition?
- Multi-Label Classification for Implicit Discourse Relation Recognition
- ConnPrompt: Connective-cloze Prompt Learning for Implicit Discourse Relation Recognition
- Encoding and Fusing Semantic Connection and Linguistic Evidence for Implicit Discourse Relation Recognition
- TEPrompt: Task Enlightenment Prompt Learning for Implicit Discourse Relation Recognition
- Infusing Hierarchical Guidance into Prompt Tuning: A Parameter-Efficient Framework for Multi-level Implicit Discourse Relation Recognition
Cite
@inproceedings{zhang2021context,
title = {{Context Tracking Network: Graph-based Context Modeling for Implicit Discourse Relation Recognition}},
author = {Zhang, Yingxue and Meng, Fandong and Li, Peng and Jian, Ping and Zhou, Jie},
booktitle = {Proceedings of the 2021 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies},
year = {2021},
doi = {10.18653/v1/2021.naacl-main.126},
url = {https://doi.org/10.18653/v1/2021.naacl-main.126}
}References
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