Reasoning Over Semantic-Level Graph for Fact Checking
Summary
Automated fact checking means judging whether a textual claim is supported or contradicted by evidence, and that evidence is often spread across several sentences. Earlier systems either glued evidence sentences into one string or combined features of each sentence separately. Both approaches miss the semantic links between facts in different sentences. The authors instead build a graph from the evidence using semantic role labeling (SRL). Its nodes are verbs, arguments, and location and time phrases. Edges connect elements within one SRL tuple and also link textually overlapping phrases across tuples. Two mechanisms inject this structure into XLNet. First, word distances are recomputed from graph connectivity, so semantically linked words count as close. Second, a graph convolutional network spreads information between nodes and a graph attention network pools it for the final decision. On FEVER, both mechanisms improved results, and the full system ranked first on the public leaderboard for label accuracy and FEVER score when the paper was submitted. The work shows that explicit semantic structure adds value on top of strong pre-trained encoders. (The excerpt provided omits the exact scores.)
Key points
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Dataset and task: FEVER has 185,445 claims checked against Wikipedia. Each claim is labelled SUPPORTED, REFUTED or NOT ENOUGH INFO. Systems are evaluated by three-way accuracy and by FEVER score, which also requires retrieving the correct evidence.
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Pipeline: document retrieval, then selection of the top-k evidence sentences, then claim verification. The graph-based verifier is the main contribution.
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Graph construction: sentences are parsed with the AllenNLP SRL tool, a re-implementation of the BERT-based model of Shi and Lin (2019). Nodes in different tuples are linked if one of three conditions holds:
- they are identical;
- one contains the other;
- their word overlap is more than half the length of the shorter phrase.
The claim is turned into a graph with the same procedure.
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Model: XLNet is the backbone, with graph-based relative distances, followed by a GCN for propagation and a GAT for aggregation. Ablation experiments confirm that each graph component helps.
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Error source and future work: irrelevant retrieved evidence can mislead the verifier. One example is a film titled "The Gifted" being confused with a TV series of the same name. Joint training of evidence selection and verification is proposed as future work.
Cited by
- FacTool: Factuality Detection in Generative AI -- A Tool Augmented Framework for Multi-Task and Multi-Domain Scenarios
- CLIMATE-FEVER: A Dataset for Verification of Real-World Climate Claims
- A Survey on Automated Fact-Checking
- A Survey on Stance Detection for Mis- and Disinformation Identification
- Explainable Automated Fact-Checking for Public Health Claims
- Fine-grained Fact Verification with Kernel Graph Attention Network
- Fact-Checking Complex Claims with Program-Guided Reasoning
Cite
@inproceedings{zhong2020reasoning,
title = {{Reasoning Over Semantic-Level Graph for Fact Checking}},
author = {Zhong, Wanjun and Xu, Jingjing and Tang, Duyu and Xu, Zenan and Duan, Nan and Zhou, Ming and Wang, Jiahai and Yin, Jian},
booktitle = {Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics},
year = {2020},
doi = {10.18653/v1/2020.acl-main.549},
url = {https://doi.org/10.18653/v1/2020.acl-main.549}
}References
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