I. Introduction
A recommender system is an important and attractive domain in information filtering systems that aims at predicting the preference or the rating of active users of a given item. A recommender system can be a powerful engine employing various techniques to recommend the most relevant items for a set of users based on their past behaviors and tastes. In past decades, each of the online-based companies specializing in Internet-related services and/or products integrate a recommender system with a specific recommendation strategy. For examples, Netflix makes recommendations for a user based on the habits of watching and searching of similar users. A social network such as LinkedIn and Facebook recommends (suggests) new friends by comparing the networks of connections between different users and their friends.