A Statistical Parsing Framework for Sentiment Classification

Abstract

We present a statistical parsing framework for sentence-level sentiment classification in this article. Different from previous work employing linguistic parsing results for sentiment analysis, we develop a statistical parser to directly analyze the sentiment structure of a sentence. We show that the complicated phenomena in sentiment analysis (e.g., negation, intensification, and contrast) can be elegantly handled the same as simple and straightforward sentiment expressions in a unified and probabilistic way. We formulate the sentiment grammar upon Context-Free Grammars (CFGs), and provide a formal description of the sentiment parsing framework. We develop the parsing model to obtain the possible sentiment parsing trees for a sentence, from which the computation model is proposed to derive the sentiment strength and polarity, and the ranking model is dedicated to selecting the best sentiment tree. We train the parser directly from examples of sentences annotated only with sentiment polarity labels but without any syntactic annotations or polarity annotations of the constitutes within the sentences. Therefore we can obtain the training data easily. In particular, we train a sentiment parser, s.parser, from a large amount of review sentences with users' ratings as rough sentiment polarity labels. Extensive experiment results on existing benchmark datasets show significant improvements over baseline sentiment classification approaches.