... Concerning the recommender type, six works are classified as CB by their authors (Guan et al., 2017;Koch & Landes, 2014;Serrano, Romero, & Olivas, 2013;Torre & Torsani, 2016;Valentin, Emrich, Lahann, Werth, & Loos, 2015;Wan & Niu, 2018), four proposals are considered CF (Aimeur, Onana, & Saleman, 2007;Bakhshinategh, Spanakis, Zaiane, & Elatia, 2017;Capuano, Gaeta, Ritrovato, & Salerno, 2014;Santos & Boticario, 2008), six researches are KB (Baneres & Conesa, 2017; Emmenegger et al., 2016;Florian & Fabregat, 2011;Harrathi, Touzani, & Braham, 2018;Mao, Shou, Fan, Chen, & Kankanhalli, 2015;Paquette, 2016), one system is treated as UB (Sielis et al., 2011) and the rest are cataloged as hybrid approaches. With regard to the domain, we classify the proposals into: (1) health domain (Khobreh, Ansari, Dornhofer, & Fathi, 2013), (2) communication domain (Guan et al., 2017;Mao et al., 2015;Torre & Torsani, 2016), (3) social media domain (Duran, Chanchi, Arciniegas, & Baldassarri, 2016;Valentin et al., 2015), (4) employment domain (Baneres & Conesa, 2017;Damiani et al., 2015;Isaias, Casaca, & Pifano, 2010;Wang, 2016) and general domain (the rest of proposals). ...