Utari, Retno Endah, and Bullion Dragon Andah. “PENGARUH PENERAPAN ELECTRONIC CUSTOMER RELATIONSHIP MANAGEMENT TERHADAP UPAYA PENINGKATAN LOYALITAS WALI MURID SMK MUHAMMADIYAH 9 JAKARTA”. IDEALIS : InDonEsiA JournaL Information System, vol. 1, no. 3, July 2018, pp. 390-5, https://jom.fti.budiluhur.ac.id/IDEALIS/article/view/1276.