  Given a target name, which can be a product aspect or entity, identifying its
aspect words and opinion words in a given corpus is a fine-grained task in
target-based sentiment analysis (TSA). This task is challenging, especially
when we have no labeled data and we want to perform it for any given domain. To
address it, we propose a general two-stage approach. Stage one extracts/groups
the target-related words (call t-words) for a given target. This is relatively
easy as we can apply an existing semantics-based learning technique. Stage two
separates the aspect and opinion words from the grouped t-words, which is
challenging because we often do not have enough word-level aspect and opinion
labels. In this work, we formulate this problem in a PU learning setting and
incorporate the idea of lifelong learning to solve it. Experimental results
show the effectiveness of our approach.
