which subclass of information filtering system was work of John Thomas Riedl
John T. Riedl:  His published works include highly influential research on the social web, recommendation systems, and collaborative systems. Recommender system: A recommender system or a recommendation system (sometimes replacing "system" with a synonym such as platform or engine) is a subclass of information filtering system that seeks to predict the "rating" or "preference" that a user would give to an item.
A recommender system