Towards Building a Competitive Opinion Summarization System: Challenges and Keys Elena Lloret author Alexandra Balahur author Manuel Palomar author Andrés Montoyo author 2009-06 text Proceedings of Human Language Technologies: The 2009 Annual Conference of the North American Chapter of the Association for Computational Linguistics, Companion Volume: Student Research Workshop and Doctoral Consortium Ulrich Germann editor Chirag Shah editor Svetlana Stoyanchev editor Carolyn Penstein Rosé editor Anoop Sarkar editor Association for Computational Linguistics Boulder, Colorado conference publication lloret-etal-2009-towards https://aclanthology.org/N09-3013/ 2009-06 72 77