Ahmad El Sayed, Hakim Hacid, Djamel A. Zighed. Exploring Validity Indices for Clustering Textual Data. In Djamel A. Zighed, Shusaku Tsumoto, Zbigniew W. Ras, Hakim Hacid, editors, Mining Complex Data. Volume 165 of Studies in Computational Intelligence, pages 281-300, Springer, 2009. [doi]