Opinion Word Expansion and Target Extraction through Double Propagation Guang Qiu author Bing Liu author Jiajun Bu author Chun Chen author 2011-03 text journal article Computational Linguistics continuing MIT Press Cambridge, MA periodical academic journal qiu-etal-2011-opinion 10.1162/coli_a_00034 https://aclanthology.org/J11-1002/ 2011-03 37 1 9 27