A Unified Linear-Time Framework for Sentence-Level Discourse Parsing
Summary
Lin et al. address sentence-level discourse analysis under Rhetorical Structure Theory (RST). This involves two steps: splitting a sentence into elementary discourse units (EDUs) and assembling them into a labeled discourse tree. Earlier systems faced a trade-off. Greedy shift-reduce parsers run fast but decide from local context. Chart parsers search globally but scale cubically.
The authors close this gap with a fully neural framework built on Pointer Networks, using no hand-engineered features. The segmenter points to EDU boundaries. The parser works top-down and depth-first, using a stack of spans. At each step it selects a split point and then classifies the relation and nuclearity of the two new spans. Because the encoder sees the whole sentence, the decoder keeps a global view while the number of steps stays linear in the number of EDUs. A shared encoder also lets both components be trained jointly.
On RST-DT, both the segmenter and the parser clearly beat earlier systems and come close to human agreement. They also run several times faster. This makes accurate discourse structure practical as a building block for document-level parsing and for downstream tasks.
Key points
- Evaluated on the RST Discourse Treebank (RST-DT). The segmenter reaches 95.4 F1, cutting relative error by about 32% versus the prior best segmenter.
- With gold EDUs, the parser scores 81.3 F1 on relation labeling. Joint training raises this to 97.44 / 91.34 / 81.70 F1 on Span / Nuclearity / Relation, exceeding human agreement on span and nuclearity (human: 98.3 segmentation, 83.0 relation).
- The end-to-end pipeline (segmenter→parser, joint training) achieves 77.5 relation F1, about 10 points above the DCRF baseline (67.5). This even beats DCRF run on gold segmentation (77.1).
- Speed: on GPU, the segmenter is about 6.8x faster than SPADE, the parser about 3.9x faster than CODRA, and the full system about 5.9x faster than the fastest open-source system. The system remains the fastest even on CPU.
- Most confusions occur between semantically close relations, such as CAUSE vs. EXPLANATION and COMPARISON vs. CONTRAST. Code is released at ntunlpsg.github.io/project/parser/pointer-net-parser.
Cited by
- Where Are We in Discourse Relation Recognition?
- Bilingual Rhetorical Structure Parsing with Large Parallel Annotations
- A Distance-Aware Multi-Task Framework for Conversational Discourse Parsing
- Unleashing the Power of Neural Discourse Parsers - A Context and Structure Aware Approach Using Large Scale Pretraining
- A Simple and Strong Baseline for End-to-End Neural RST-style Discourse Parsing
- Top-down Discourse Parsing via Sequence Labelling
- Multilingual Neural RST Discourse Parsing
- Neural Generative Rhetorical Structure Parsing
- Can we obtain significant success in RST discourse parsing by using Large Language Models?
- DisSent: Learning Sentence Representations from Explicit Discourse Relations
- RST Discourse Parsing with Second-Stage EDU-Level Pre-training
- A Top-down Neural Architecture towards Text-level Parsing of Discourse Rhetorical Structure
- Adversarial Learning for Discourse Rhetorical Structure Parsing
Cite
@inproceedings{lin2019unified,
title = {{A Unified Linear-Time Framework for Sentence-Level Discourse Parsing}},
author = {Lin, Xiang and Joty, Shafiq and Jwalapuram, Prathyusha and Bari, M Saiful},
booktitle = {Proceedings of the 57th Annual Meeting of the Association for Computational Linguistics},
year = {2019},
doi = {10.18653/v1/p19-1410},
eprint = {1905.05682},
archivePrefix = {arXiv},
url = {https://doi.org/10.18653/v1/p19-1410}
}References
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