which subclass of information filtering system was work of John Thomas Riedl
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.
Discovery system A discovery system may be an artificial intelligence system (in the context of computer science, logic, and mathematics) or a bibliographical search system (in the context of library and information science).