Extending Implicit Discourse Relation Recognition to the PDTB-3
Summary
The PDTB-3 adds many discourse relations, and most of the new ones fall inside single sentences. Some implicit relations are also now annotated alongside explicit connectives. Shallow discourse parsers built on the PDTB-2 assumed that non-explicit relations hold only between adjacent sentences, so their main difficulty was assigning senses. Liang, Zhao and Webber show that a PDTB-3 parser must also locate implicit relations. They argue that this extra work pays off, because intra-sentential, inter-sentential and explicit-linked implicit relations have distinct sense distributions that can guide sense classification. The authors document these distributional differences and build sense classifiers on an LSTM-based Basic Model, including variants specialised by relation location. They also add a simple recognizer that flags explicit relations carrying a co-occurring implicit relation. Their results indicate that knowing where an implicit relation sits improves sense labelling. The methods are not intended to be state-of-the-art. Instead, they provide a non-trivial baseline for future PDTB-3 shallow discourse parsers.
Key points
- The PDTB-3 adds roughly 12.5K intra-sentential and about 1K inter-sentential relations compared with the PDTB-2. Over 95% of the new relations are sentence-internal, and 5780 of them are implicit.
- The Basic Model encodes each argument with an LSTM followed by max-pooling, then passes the result through hidden, dense and softmax layers. It uses 300-dimension word2vec embeddings and a hidden size of 100.
- Linked implicits are detected with an NLTK naive Bayes classifier. Its binary features are the 100 most frequent syntactic production rules. Recall for linked relations is low, since stand-alone relations dominate the data.
- In the test set (WSJ Section 23), linked implicits mostly attach to conjoined clauses or VPs, and 81.08% are signalled by "and". All recognized linked implicits are intra-sentential.
- On these recognized linked relations, the intra-sentential classifier reaches an F1 of 75, compared with 68.182 for the Basic Model.
Cited by
- Where Are We in Discourse Relation Recognition?
- The Change that Matters in Discourse Parsing: Estimating the Impact of Domain Shift on Parser Error
- The DISRPT 2023 Shared Task on Elementary Discourse Unit Segmentation, Connective Detection, and Relation Classification
- discopy: A Neural System for Shallow Discourse Parsing
- Facilitating Contrastive Learning of Discourse Relational Senses by Exploiting the Hierarchy of Sense Relations
- DiscoGeM: A Crowdsourced Corpus of Genre-Mixed Implicit Discourse Relations
- Prompt-based Logical Semantics Enhancement for Implicit Discourse Relation Recognition
- Revisiting Shallow Discourse Parsing in the PDTB-3: Handling Intra-sentential Implicits
Cite
@inproceedings{liang2020extending,
title = {{Extending Implicit Discourse Relation Recognition to the PDTB-3}},
author = {Liang, Li and Zhao, Zheng and Webber, Bonnie},
booktitle = {Proceedings of the First Workshop on Computational Approaches to Discourse},
year = {2020},
doi = {10.18653/v1/2020.codi-1.14},
eprint = {2010.06294},
archivePrefix = {arXiv},
url = {https://doi.org/10.18653/v1/2020.codi-1.14}
}References
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