How much progress have we made on RST discourse parsing? A replication study of recent results on the RST-DT
What it is about
Eight papers from 2013 to 2017 reported large gains in RST discourse parsing, with a claimed relative error reduction of 24 to 51%. The gains were attributed to distributed (neural) representations of discourse units. The authors asked the authors of nine parsers for their test-set predictions on the RST-DT, which has 385 articles (347 for training, 38 for test), and re-scored them. Their main finding is that most of the reported gains come from evaluation differences. The neural parsers were scored with macro-averaged F1 across documents, while the older parsers used micro-averaged F1. Under the same micro-averaged procedure the neural group loses its lead on the span and nuclearity scores. Its best gain on relations and full labels is 0.9 and 1.4 points, a relative error reduction of 11% and 16%. A second check used the standard Parseval procedure on right-heavy binarised trees instead of RST-Parseval. Under it the best full-label F1 is 46.3, and the gains are at most 16% relative error reduction.
Ideas
- I1.
coref/src/eval.rsand any future discourse scorer: always report micro and macro averages side by side, computed from BTreeMap-ordered per-document counts, and refuse a claim of gain unless both are stated. The paper's whole finding depends on this. - I2. A replication step before any claim of progress: keep the previous run's predictions and re-score them with the new scorer. A gain that appears only with the new scorer is an evaluation artefact, the paper's main lesson.
- I3. Add a standard Parseval mode for Mova's own discourse trees: right-heavy binarisation of the reference, then labelled attachment decisions. Compare it with the native scorer on the same output to see how much the scorer matters.
- I4. Keep a simple feature baseline (unit length, distance between units, word and POS n-grams, as in the paper's first group) in every discourse measurement. The paper shows such a baseline is competitive, so a new rule system must beat it on the same scorer.
For Mova
The chapters are 36. Discourse relations and coherence (relations and structure) and 38. Dialogue, discourse markers and reported speech (markers). The code is coref/src/eval.rs as the model for scorer conventions, and prag/src/frames.rs for the discourse layer. Mova has no RST parser in the repo; if one is built, the measure is the paper's table layout (S, N, R, F) with both averages, run twice, plus the replication check against the old predictions. The RST-DT is evaluation-only data.
Cite
@inproceedings{morey2017how,
title = {{How much progress have we made on RST discourse parsing? A replication study of recent results on the RST-DT}},
author = {Morey, Mathieu and Muller, Philippe and Asher, Nicholas},
booktitle = {Proceedings of the 2017 Conference on Empirical Methods in Natural Language Processing},
year = {2017},
doi = {10.18653/v1/d17-1136},
url = {https://doi.org/10.18653/v1/d17-1136}
}References
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