Many types of recommender systems exist such as non-personalized, demographic, content based, content based, collaborative (user based), collaborative (item based) and model based. Item based collaborative models have been applied successfully in commercial settings thanks to scalability and quality advantages as compared to others. Model based approaches differ from the rest which rely on memory of events. Instead they involve the creation of a probabilistic, decision tree or neural net model that attempts to identify the underlying logic to users’ choices.