Zero-shot transfer for implicit discourse relation classification
Summary
Implicit discourse relations link two text spans without an explicit connective such as "because," and they are the hardest part of discourse parsing. Most languages have no annotated data for this task. Kurfalı and Östling offer what they describe as the first zero-shot approach. Each argument is encoded with frozen, pre-trained multilingual LASER sentence embeddings. The two vectors are combined DisSent-style (concatenation, mean, difference, element-wise product) and passed to a small feedforward network. Four one-versus-rest classifiers cover the top-level PDTB senses. Training uses English PDTB 3.0, optionally adding the Turkish Discourse Bank (TDB). Testing uses TED-MDB, a parallel corpus of TED talks annotated under PDTB 3.0 guidelines.
On TED-MDB, scores in languages with no training data are close to those for English, so transfer costs little accuracy. Pooling English and Turkish training data significantly beats English-only training for every test language. The method needs no discourse annotation in the target language, so it could in principle cover the roughly hundred languages LASER supports. This makes it relevant to low-resource languages such as Ukrainian.
Key points
- Data: PDTB 2.0 serves as a sanity check against prior work, and PDTB 3.0 is the main training set. TDB (about 40,000 words, 649 implicit training relations) is added for pooling. TED-MDB (six TED talks) is used only for evaluation in English, German, Lithuanian, Polish, Portuguese, Russian and Turkish.
- Same-language baseline (PDTB 2.0 test, F1): Comparison 28.19, Contingency 50.63, Expansion 64.07, Temporal 29.22. These scores are below state of the art but adequate as a starting point.
- English-only training (PDTB 3.0): The average F1 is 45.23 on the PDTB 3.0 test set. On TED-MDB it ranges from 33.52 (Turkish) to 40.96 (English).
- Pooled training (PDTB 3.0 + TDB): Average F1 rises for every TED-MDB language compared with English-only training, for example Russian 35.00 → 38.23 and German 39.22 → 41.44. Each setup was run 100 times, and the gains are significant (Mann-Whitney U, p < 0.001). Most of the improvement comes from Expansion.
- Implementation: The code is written in PyTorch and released at github.com/MurathanKurfali/multilingual IDRC. It uses a 100-unit hidden layer, dropout 0.3, the AdaGrad optimizer and balanced negative sampling in each epoch.
Cited by
- Where Are We in Discourse Relation Recognition?
- What Causes the Failure of Explicit to Implicit Discourse Relation Recognition?
- Revisiting Shallow Discourse Parsing in the PDTB-3: Handling Intra-sentential Implicits
Cite
@inproceedings{kurfal2019zero,
title = {{Zero-shot transfer for implicit discourse relation classification}},
author = {Kurfalı, Murathan and Östling, Robert},
booktitle = {Proceedings of the 20th Annual SIGdial Meeting on Discourse and Dialogue},
year = {2019},
doi = {10.18653/v1/w19-5927},
url = {https://doi.org/10.18653/v1/w19-5927}
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