  Aspect based sentiment analysis, predicting sentiment polarity of given
aspects, has drawn extensive attention. Previous attention-based models
emphasize using aspect semantics to help extract opinion features for
classification. However, these works are either not able to capture opinion
spans as a whole, or not able to capture variable-length opinion spans. In this
paper, we present a neat and effective structured attention model by
aggregating multiple linear-chain CRFs. Such a design allows the model to
extract aspect-specific opinion spans and then evaluate sentiment polarity by
exploiting the extracted opinion features. The experimental results on four
datasets demonstrate the effectiveness of the proposed model, and our analysis
demonstrates that our model can capture aspect-specific opinion spans.
