Abstract
Recommender systems suggest the most appropriate items to users in order to help customers to find the most relevant items and facilitate sales. Collaborative filtering recommendation algorithm is the most successful technique for recommendation. In view of the fact that collaborative filtering systems depend on neighbors as the source of information, the recommendation quality of this approach depends on the neighbor's selection. However, selecting neighbors can either stem from similarity or trust metrics. In this paper, we analyze these two types of neighbor's selection metrics used in the field of recommendation in the literature. For each type, we first define it and then review different proposed metrics.