Gennaro Costagliola Vittorio Fuccella Massimiliano Giordano Giuseppe Polese Monitoring Online Tests through Data Visualization. 773-784 2009 21 IEEE Trans. Knowl. Data Eng. 6 http://dx.doi.org/10.1109/TKDE.2008.133 db/journals/tkde/tkde21.html#CostagliolaFGP09