Elena Lloret Alexandra Balahur Manuel Palomar Andrés Montoyo Towards Building a Competitive Opinion Summarization System: Challenges and Keys. 72-77 2009 HLT-NAACL (Student Research Workshop and Doctoral Consortium) http://www.aclweb.org/anthology/N09-3013 conf/naacl/2009d db/conf/naacl/naacl2009d.html#LloretBPM09