Presentation held during the NKUA postgraduate course “DATA BASES MANAGEMENT SYSTEMS” on 6th of December 2016 at National and Kapodistrian University of Athens. Gerasimos Antzoulatos, i2S Charalampos Dimitrakopoulos, CITE Dimitris Katris, UoA Giota Koltsida, UoA Nikolas Laskaris , UoA Eleni Petra, UOA Stella Tsani, Prof. Phoebe Koundouri, ICRE8 http://bit.ly/2hEkn3G