First Author:   Olfa Frini ISCAE Manouba University Tunisia; ECSTRA Carthage University Tunisia frini.olfa@planet.tn   frini.olfa@planet.tn Ezzahra, 2034, Tunisia   +216098350451(Phone) +216098350451(Fax) Second Author: Khoutem Ben Jedidia ISCAE Manouba University khoutembj@yahoo.fr   Mourouj 4, 2074., Tunisia   +21698945905(Phone)