Sentence-level sentiment analysis
Document-level sentiment classification is too coarse for most applications.
Let us move to the sentence level.
Much of the work on sentence level sentiment analysis focuses on identifying subjective sentences in news articles.
Classification: objective and subjective.
All techniques use some forms of machine learning.
E.g., using a naïve Bayesian classifier with a set of data features/attributes extracted from training sentences (Wiebe et al. ACL-99).