Integrating Deep Event-Level and Script-Level Information for Script Event Prediction
Summary
The paper addresses script event prediction. Given a chain of events that have already occurred, the model must choose the next event from several candidates. The authors point out two shortcomings of earlier approaches. First, an event was usually reduced to a verb and the head words of its participants, so other useful contextual details were lost. Second, only a single event sequence centered on one protagonist was considered. To address both shortcomings, they propose MCPredictor, a Transformer-based model. At the level of an individual event, it combines a vector representation of the tuple (verb and participants) with an encoding of the source sentence produced by BERT-tiny. At the script level, the model builds a separate chain for each participant of the candidate event. An attention mechanism weights the scores of these chains. Experiments were conducted on the New York Times corpus, and according to the authors, the model outperforms previous approaches. The work shows that sentence context and the perspectives of multiple participants noticeably improve event modeling.
Key points
- An event is represented as a tuple: verb, subject, object, indirect object, and the sentence from which it was extracted. Missing participants are filled with null. Candidates have no sentence of their own.
- The model has four components: event encoding, text encoding (the "[CLS]" output of BERT-tiny), chain modeling with a stack of Transformer layers, and attention-based scoring that aggregates multiple chains. To prevent information leakage, the other events of the chain in the sentence are replaced with "[UNK]", and the protagonist's role is marked with the tags [subj]/[obj]/[iobj].
- On the NYT development set, the full model with all sentence components achieves an accuracy of 67.35 %. Masking verbs lowers accuracy by 6.81 points, masking nouns by 2.54, and masking both verbs and nouns by 11.99.
- Masking the verb of the event itself has almost no effect on the result (−0.06), because this information is already present in the tuple encoding. In contrast, masking the remaining verbs in the sentence reduces accuracy by 6.45 points.
- Among the limitations, the authors note that the candidate's participants must be known in advance. Otherwise, combinations of entities have to be enumerated, which is costly.
Cite
@inproceedings{bai2021integrating,
title = {{Integrating Deep Event-Level and Script-Level Information for Script Event Prediction}},
author = {Bai, Long and Guan, Saiping and Guo, Jiafeng and Li, Zixuan and Jin, Xiaolong and Cheng, Xueqi},
booktitle = {Proceedings of the 2021 Conference on Empirical Methods in Natural Language Processing},
year = {2021},
doi = {10.18653/v1/2021.emnlp-main.777},
eprint = {2110.15706},
archivePrefix = {arXiv},
url = {https://doi.org/10.18653/v1/2021.emnlp-main.777}
}References
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