Abstract: Causality represents a kind of correlation between cause and effect, where the happening of cause will leads to the happening of effect. As the most important type of relationship between entities, causality plays a vital role in many fields such as automatic reasoning and scenario generation. Therefore, extracting causal relation becomes a basic task in natural language processing and text mining. Different from traditional text classification methods or relation extraction methods, this paper proposes a sequence labeling method to extract causal entity in text and identify direction of causality, without relying on feature engineering or causal background knowledge. The main contributions of this paper can be summarized as follows: 1) we extend syntactic dependency tree to the syntactic dependency graph, adopt graph attention networks in natural language processing, and introduce the concept of S-GAT(graph attention network based on syntactic dependency graph); 2) Bi-LSTM+CRF+S-GAT model for causal extraction is proposed, which generates causal label of each word in sentence based on input word vectors; 3) SemEval data set is modified and extended, and rules are defined to relabel experimental data with an aim of overcoming defects of the original labeling method. Extensive experiments are conducted on the expanded SemEval dataset, which shows that our model achieves 0.064 improvement over state-of-the-art model Bi-LSTM+CRF+self-ATT in terms of prediction accuracy.

Key words: causal relation extraction, graph attention networks (GATs), sequence labeling, syntactic dependency graph, bidirectional long short-term memory (Bi-LSTM)