López Carreño, R., and J. V. Rodríguez Muñoz. “A Classification of Added Value Services in Mass Media Portals”. Scire: Knowledge Representation and Organization (ISSNe 2340-7042; ISSN 1135-3716), vol. 9, no. 2, June 2003, pp. 111-22, doi:10.54886/scire.v9i2.1470.