Wen Zhou Zongtian Liu Yan Zhao Concept Hierarchies Generation for Classification using Fuzzy Formal Concept Analysis. 50-55 2007 SNPD (3) http://doi.ieeecomputersociety.org/10.1109/SNPD.2007.215 conf/snpd/2007 db/conf/snpd/snpd2007-3.html#ZhouLZ07