Pythagoras Karampiperis Demetrios G. Sampson Towards Next Generation Activity-Based Web-Based Educational Systems. 868-872 2005 conf/icalt/2005 ICALT http://doi.ieeecomputersociety.org/10.1109/ICALT.2005.291 db/conf/icalt/icalt2005.html#KarampiperisS05a