Aggregation of opinion words (Hu and Liu, KDD-04; Ding and Liu, 2008)
Input: a pair (f, s), where f is a product feature and s is a sentence that contains f.
Output: whether the opinion on f in s is positive, negative, or neutral.
Step 1: split the sentence if needed based on BUT words (but, except that, etc).
Step 2: work on the segment sf containing f. Let the set of opinion words in sf be w1, .., wn. Sum up their orientations (1, -1, 0), and assign the orientation to (f, s) accordingly.
In (Ding and Liu, SIGIR-07), step 2 is changed to
with better results. wi.o is the opinion orientation of wi. d(wi, f) is the distance from f to wi.