Two Differentially Private Rating Collection Mechanisms for Recommender Systems

Recommender Systems (RS) [1] are a kind of system that seek to recommend to users what they are likely interested in. Unlike search engines, the users do not need to type any keyword. The RS's will learn their interest automatically. For instance, if the user has just bought a numeric camera, the RS will recommend to him some SD memory cards; if a user watches a lot of action movies, the RS may suggest some other action movies to him. And this is the typical behaviors which we observe universally in Netflix (movies), Youtube (videos), Google Play (apps), Facebook (friends), Amazon (goods) and other platforms today.