6. A computer system for performing sentiment analysis, the computer system comprising: a processor that is adapted to execute stored instructions; and a memory device that stores instructions, the memory device comprising: computer-implemented code adapted to perform a first sentiment analysis on microblogging data based on an opinion lexicon that includes non-domain-specific opinion terms, to generate first training data; computer-implemented code adapted to train a classifier using the first training data; computer-implemented code adapted to perform a statistical test on results of the first sentiment analysis on the microblogging data to identify a new opinion term, the new opinion term being domain-specific to the microblogging data; computer-implemented code adapted to add the new opinion term to the opinion lexicon to grow the opinion lexicon so that the opinion lexicon includes domain-specific opinion terms; computer-implemented code adapted to identify new microblogging data other than the microblogging data on which the first sentiment analysis has been performed, based on the opinion lexicon to which the new opinion term has been added; computer-implemented code adapted to perform a second sentiment analysis on the new microblogging data using the classifier to generate second training data; and computer-implemented code adapted to retrain the classifier as has been trained using the first training data, using the second training data to improve the classifier.
6. A computer system for performing sentiment analysis, the computer system comprising: a processor that is adapted to execute stored instructions; and a memory device that stores instructions, the memory device comprising: computer-implemented code adapted to perform a first sentiment analysis on microblogging data based on an opinion lexicon that includes non-domain-specific opinion terms, to generate first training data; computer-implemented code adapted to train a classifier using the first training data; computer-implemented code adapted to perform a statistical test on results of the first sentiment analysis on the microblogging data to identify a new opinion term, the new opinion term being domain-specific to the microblogging data; computer-implemented code adapted to add the new opinion term to the opinion lexicon to grow the opinion lexicon so that the opinion lexicon includes domain-specific opinion terms; computer-implemented code adapted to identify new microblogging data other than the microblogging data on which the first sentiment analysis has been performed, based on the opinion lexicon to which the new opinion term has been added; computer-implemented code adapted to perform a second sentiment analysis on the new microblogging data using the classifier to generate second training data; and computer-implemented code adapted to retrain the classifier as has been trained using the first training data, using the second training data to improve the classifier. 7. The computer system recited in claim 6 , wherein the computer-implemented code adapted to train the classifier comprises computer-implemented code adapted to: identify the new opinion term and microblogging data based on a Pearsons chi-square value; select a text window comprising an entity of the new microblogging data; select one or more features from the text window; and train the classifier to determine a sentiment polarity for the entity.