Discourse Parsing with Attention-based Hierarchical Neural Networks
Written for the Research library (claude-opus-5-5) from the paper text. Original — aclanthology.org/D16-1035.pdf
Summary
The paper tackles document-level discourse parsing under Rhetorical Structure Theory (RST), where a text is organized into a tree. The leaves of this tree are Elementary Discourse Units (EDUs), and its inner nodes carry nuclearity and rhetorical relations. Strong earlier systems relied heavily on hand-engineered features, and the only neural approach was a recursive network that struggles with long inputs. The authors build span representations in two levels. A bi-LSTM over words and POS tags encodes each EDU, and a second bi-LSTM over EDUs encodes a whole span. An attention layer then highlights the most informative EDUs. For a pair of adjacent spans, a factorized tensor layer captures multiplicative interactions between their features. Three classifiers then decide whether to merge the spans, which side is the nucleus, and what relation holds between them. A probabilistic CKY-style parser, sped up with two levels of caching, assembles the tree. On RST-DT the system matches state-of-the-art results with minimal manual features and achieves the top span score. This suggests that neural models can compete in a task long dominated by feature engineering.
Key points
- Evaluated on RST-DT, which contains 385 Wall Street Journal articles split into 347 for training and 38 for testing.
- The full model scores S 85.8, N 71.1 and R 58.9, the best span result among the compared systems. Human agreement is S 88.7, N 77.7 and R 65.8.
- Without handcrafted features, the model reaches S 84.2, N 70.4 and R 56.3. The recursive model of Li et al. (2014a) scores S 82.4, N 69.2 and R 56.8 under the same condition, so the new model is better on span and nucleus but slightly lower on relation.
- To limit parameters and computation, each tensor slice is approximated by the product of two low-rank matrices, following Pei et al. (2014).
- A qualitative attention example on a Contrast relation shows the model giving the most weight (0.49) to the EDU that carries the main meaning.
Cited by
- How much progress have we made on RST discourse parsing? A replication study of recent results on the RST-DT
- A Dependency Perspective on RST Discourse Parsing and Evaluation
- GumDrop at the DISRPT2019 Shared Task: A Model Stacking Approach to Discourse Unit Segmentation and Connective Detection
Cite
@inproceedings{li2016discourse,
title = {{Discourse Parsing with Attention-based Hierarchical Neural Networks}},
author = {Li, Qi and Li, Tianshi and Chang, Baobao},
booktitle = {Proceedings of the 2016 Conference on Empirical Methods in Natural Language Processing},
year = {2016},
doi = {10.18653/v1/d16-1035},
url = {https://doi.org/10.18653/v1/d16-1035}
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