A Novel Cascade Binary Tagging Framework for Relational Triple Extraction
Summary
Relational triple extraction pulls (subject, relation, object) facts out of raw sentences, a core step in building knowledge graphs. It becomes difficult when several triples in one sentence share entities, as in the EntityPairOverlap (EPO) and SingleEntityOverlap (SEO) patterns. Earlier joint approaches, such as Seq2Seq models with copying or the GCN-based GraphRel, still assign a relation label to each entity pair. That design suffers from heavy class imbalance and gets confused when one entity takes part in several facts.
The authors define the training likelihood directly over whole triples. They then treat every relation as a mapping from a subject to its object(s), which may be empty. Their model, CasRel, works in two stages on top of a BERT encoder:
- it first marks subject spans;
- for each detected subject, it runs one binary object tagger per relation.
On the public NYT and WebNLG datasets, CasRel beats the strongest earlier systems by a wide margin. Even with a randomly initialized encoder it already outperforms them. The gains hold across all overlap types and are largest for sentences containing many triples, which makes the method well suited to dense, entity-rich text.
Key points
- Core idea: instead of a classifier f(s, o) → r, CasRel learns one tagger per relation, f_r(s) → o. This lets the model handle overlapping triples without extra machinery.
- With a pre-trained BERT encoder, CasRel exceeds the best baseline by 17.5 F1 points on NYT and 30.2 F1 points on WebNLG. The variants CasRel_random and CasRel_LSTM also stay strong on both datasets.
- Baselines do much worse on WebNLG, where EPO and SEO sentences dominate, than on NYT, where most sentences are Normal. CasRel performs consistently on both.
- For sentences with five or more triples, CasRel reaches an F1 of 83.7 on NYT and 90.9 on WebNLG. This is +37.8 and +35.2 over CopyR_RL, the strongest baseline in that comparison.
- Code and data are released at github.com/weizhepei/CasRel (ACL 2020).
Cited by
- TPLinker: Single-stage Joint Extraction of Entities and Relations Through Token Pair Linking
- ChatIE: Zero-Shot Information Extraction via Chatting with ChatGPT
Cite
@inproceedings{wei2020novel,
title = {{A Novel Cascade Binary Tagging Framework for Relational Triple Extraction}},
author = {Wei, Zhepei and Su, Jianlin and Wang, Yue and Tian, Yuan and Chang, Yi},
booktitle = {Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics},
year = {2020},
doi = {10.18653/v1/2020.acl-main.136},
url = {https://doi.org/10.18653/v1/2020.acl-main.136}
}References
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