Source: http://www.ests.um5.ac.ma/cours/Dipl%C3%B4me%20Universitaire%20de%20Technologie/Techniques%20de%20Commercialisation%20et%20des%20Services/Semestre%2002/Marketing%20Op%C3%A9rationnel/Cours%20du%20Marketing%20op%C3%A9rationnel2020.pdf