Span-level Bidirectional Cross-attention Framework for Aspect Sentiment Triplet Extraction

Aspect Sentiment Triplet Extraction (ASTE) is a new fine-grained sentiment analysis task that aims to extract triplets of aspect terms, sentiments, and opinion terms from review sentences. Recently, span-level models achieve gratifying results on ASTE task by taking advantage of whole span predictions. However, all the spans generated by these methods inevitably share at least one token with some others, and these method suffer from the similarity of these spans due to their similar distributions. Moreover, since either the aspect term or opinion term can trigger a sentiment triplet, it is challenging to make use of the information more comprehensively and adequately. To address these concerns, we propose a span-level bidirectional cross-attention framework. Specifically, we design a similar span separation loss to detach the spans with shared tokens and a bidirectional cross-attention structure that consists of aspect and opinion decoders to decode the span-level representations in both aspect-to-opinion and opinion-to-aspect directions. With differentiated span representations and bidirectional decoding structure, our model can extract sentiment triplets more precisely and efficiently. Experimental results show that our framework significantly outperforms state-of-the-art methods, achieving better performance in predicting triplets with multi-token entities and extracting triplets in sentences with multi-triplets.