Srivatsan Laxman P. S. Sastry K. P. Unnikrishnan Discovering Frequent Generalized Episodes When Events Persist for Different Durations. 1188-1201 2007 19 IEEE Trans. Knowl. Data Eng. 9 http://doi.ieeecomputersociety.org/10.1109/TKDE.2007.1055 db/journals/tkde/tkde19.html#LaxmanSU07