In summary, as seen above, many recommender systems that employ traditional
content-based, knowledge-based, and hybrid techniques can be viewed as multicriteria recommender systems, since they model user preferences based on multiattribute content of items that users preferred in the past or allow users to specify their content-related preferences – i.e., search or filtering conditions for multi-
attribute content of items (e.g., identifying the preferred movie genre or providing
preferences on multiple pre-defined genre values). However, as mentioned earlier,
there is a recent trend in multi-criteria recommendation that studies innovative approaches in collaborative recommendation by engaging multi-criteria ratings. We
believe that this additional information on users’ preferences offers many opportunities for providing novel recommendation support, creating a unique multi-criteria
rating environment that has not been extensively researched. Therefore, in the following sections, we survey the state-of-the-art techniques on this particular type of
systems that use individual ratings along multiple criteria, which we will refer to as
multi-criteria rating recommenders.