Toward the next generation of recommender systems: http://scholar.google.com/scholar?hl=en&lr=&safe=off&cluster=17028412407754346902
[Passive] Collaborative Filtering: http://en.wikipedia.org/wiki/Collaborative_filtering
Recommendation System: http://en.wikipedia.org/wiki/Recommendation_system
Information Filtering System: http://en.wikipedia.org/wiki/Information_filtering
