sentence1: sentiment classification is a hot research topic in natural language processing field , and has many applications in both academic and industrial areas ( cite-p-17-1-16 , cite-p-17-1-12 , cite-p-17-3-4 , cite-p-17-3-3 ) .
sentence2: sentiment classification is a well studied problem ( cite-p-13-3-6 , cite-p-13-1-14 , cite-p-13-3-3 ) and in many domains users explicitly provide ratings for each aspect making automated means unnecessary .