“…Recently, another issue has been addressed by a couple of recent published work (Ahmed, Low, Aly, Josifovski, & Smola, 2011;Gueye, Abdessalem, & Naacke, 2012;Li, Yang, Wang, & Kitsuregawa, 2007;Xiang et al, 2010) that is referred to as the dynamicity problem. We define it as the effect of time on user's preferences and how it can be reflected in their profiles.…”