Dilhan Perera Judy Kay Irena Koprinska Kalina Yacef Osmar R. Zaïane Clustering and Sequential Pattern Mining of Online Collaborative Learning Data. 759-772 2009 21 IEEE Trans. Knowl. Data Eng. 6 http://dx.doi.org/10.1109/TKDE.2008.138 db/journals/tkde/tkde21.html#PereraKKYZ09