19. An apparatus operable to provide at least one sentiment classifier based on a plurality of features, the apparatus comprising: a processor; and a storage device, operatively connected to the processor, and having stored thereon instructions that, when executed by the processor, cause the processor to: extract the plurality of features from training data, wherein the training data comprises a plurality of units, and wherein those instructions that cause the processor to extract the plurality of features are further operative to cause the processor to: label at least one element of each unit of the training data according to a plurality of part-of-speech (PoS) tags to provide PoS features; check at least one element of each unit of the training data according to a plurality of dictionaries to provide dictionary features; detect a plurality of negation/inversion elements in the training data to provide a plurality of negation/inversion features based on a negation dictionary and an inversion dictionary of the plurality of dictionaries; and label at least one element after each of the plurality of negation/inversion features to provide negated/inverted elements features based on at least one of a propagation window or punctuation in the training data; determine a value for each feature of the plurality of features based on a frequency at which each feature occurs in the training data; label each unit of the training data according to a plurality of sentiment classes to provide labeled training data; and provide the at least one sentiment classifier based on the value of each feature of the plurality of features and the labeled training data using a supervised classification technique.
25. The apparatus of claim 19 , the storage device further comprising instructions that, when executed by the processor, cause the processor to: provide a plurality of sentiment classifiers based on a plurality of sets of training data, the plurality of sets of training data being associated with a plurality of subjects; associate each sentiment classifier of the plurality of sentiment classifiers with one of the plurality of subjects; and provide a taxonomy of sentiment classifiers based on a subject, of the plurality of subjects, associated with each sentiment classifier of the plurality of sentiment classifiers.