Samaneh Moghaddam Martin Ester Opinion digger: an unsupervised opinion miner from unstructured product reviews. 1825-1828 2010 CIKM http://doi.acm.org/10.1145/1871437.1871739 conf/cikm/2010 db/conf/cikm/cikm2010.html#MoghaddamE10