decomposed into k single-rating recommendation problems. Second, aggregation function
f is chosen using domain expertise, statistical techniques, or machine learning techniques. For example, the domain expert may suggest a simple average function of
the underlying multi-criteria ratings for each item based on her prior experience
and knowledge. An aggregation function also can be obtained by using statistical
techniques, such as linear and non-linear regression analysis techniques, as well
as various sophisticated machine learning techniques, such as artificial neural networks. Finally, the overall rating of each unrated item is computed based on the k
predicted individual criteria ratings and the chosen aggregation function f .