In most recommender systems, the utility function usually considers a single-
criterion value, e.g., an overall evaluation or rating of an item by a user. In recent
work, this assumption has been considered as limited [2, 4, 48], because the suitability of the recommended item for a particular user may depend on more than one
utility-related aspect that the user takes into consideration when making the choice.
Particularly in systems where recommendations are based on the opinion of others,
the incorporation of multiple criteria that can affect the users’ opinions may lead to
more accurate recommendations.
Thus, the additional information provided by multi-criteria ratings could help
to improve the quality of recommendations because it would be able to represent
more complex preferences of each user. As an illustration, consider the following
example. In a traditional single-rating movie recommender system, user u provides
a single rating for movie i that the user has seen, denoted by R(u, i). Specifically,
suppose that the recommender system predicts the rating of the movie that the user
has not seen based on the movie ratings of other users with similar preferences, who
are commonly referred to as “neighbors” [71]. Therefore, the ability to correctly
determine the users that are most similar to the target user is crucial in order to have
accurate predictions or recommendations. For example, if two users u and u′ have
seen three movies in common, and both of them rated their overall satisfaction from
each of the three movies as 6 out of 10, the two users are considered as neighbors
and the ratings of unseen movies for user u are predicted using the ratings of user
u′.