Hrin, T., M. Segedinac, and D. Milenkoviæ. “Development of Ontological Knowledge Representation: Learning Hydrocarbons With Double Bonds at the Secondary Level”. African Journal of Chemical Education, vol. 3, no. 2, June 2013, pp. 76-90, https://www.ajol.info/index.php/ajce/article/view/89876.