Discourse Relation Sense Classification Using Cross-argument Semantic Similarity Based on Word Embeddings
Summary
The paper describes a system built for the supplementary track of the 2016 CoNLL shared task, which focused on shallow parsing of discourse. The track asks systems to assign one of 15 hierarchically organized senses to an English discourse relation when its two arguments are already known, along with the connective if the relation is Explicit. The authors build separate models for Explicit and Non-Explicit relations. At test time, they route each item by checking whether a connective is present. The core model is a Logistic Regression classifier whose features come only from pre-trained word2vec Google News vectors. It uses averaged (centroid) embeddings of Arg1, Arg2 and the connective, plus cosine-based comparisons between the arguments: whole-argument similarity, top-N and word-alignment similarities, POS-restricted centroids, and similarity to 103 connectives from the Penn Discourse Treebank manual. For Non-Explicit senses, they also test two CNNs: Kim's sentence classifier and a modified ARC-1 matching network called ARC-1M. The lightweight LR system placed first overall. This suggests that dense embeddings combined with simple cross-argument similarity can compete with more complex designs. The code is public on GitHub.
Key points
- Official overall F-scores were 64.13 (Dev), 63.31 (Test) and 54.69 (Blind). The system ranked 1st overall, 2nd on Explicit (0.07 behind the leader) and 4th on Non-Explicit (2.75 behind). The Explicit F-score on Dev was 0.912.
- Non-Explicit results on Dev:
- Embeddings-only LR scored 35.54. Embeddings-only CNN scored 34.34 and ARC-1M scored 36.21.
- Adding similarity features raised LR to 40.32 (the submitted system).
- Adding connective similarities brought it to 40.99.
- Adding modal-verb (MD) POS similarities brought it to 41.66.
- The post-deadline additions also improved Non-Explicit on Blind by 0.36, to 34.92.
- Data sizes were as follows, with evaluation run on the TIRA platform:
- Train: 15,500 Explicit and 18,115 Non-Explicit relations.
- Dev: 740 Explicit and 782 Non-Explicit relations.
- Test: 990 Explicit and 1,026 Non-Explicit relations.
- Blind: 608 Explicit and 661 Non-Explicit relations.
- The neural models showed complementary strengths:
- ARC-1M was clearly best on Contingency.Cause.Reason and Contingency.Cause.Result.
- Kim's CNN did better on Contrast, EntRel, Conjunction and Instantiation but never predicted Expansion.Restatement.
- Rare senses such as Concession and Synchrony scored 0 for all models.
Cited by
- A Systematic Study of Neural Discourse Models for Implicit Discourse Relation
- CoNLL 2016 Shared Task on Multilingual Shallow Discourse Parsing
Cite
@inproceedings{mihaylov2016discourse,
title = {{Discourse Relation Sense Classification Using Cross-argument Semantic Similarity Based on Word Embeddings}},
author = {Mihaylov, Todor and Frank, Anette},
booktitle = {Proceedings of the CoNLL-16 shared task},
year = {2016},
doi = {10.18653/v1/k16-2014},
url = {https://doi.org/10.18653/v1/k16-2014}
}References
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