Opinion Expression Mining by Exploiting Keyphrase Extraction Gábor Berend author 2011-11 text Proceedings of 5th International Joint Conference on Natural Language Processing Haifeng Wang editor David Yarowsky editor Asian Federation of Natural Language Processing Chiang Mai, Thailand conference publication berend-2011-opinion https://aclanthology.org/I11-1130/ 2011-11 1162 1170