Whether someone likes a movie (or a song) is usually subjective, often emotional, and can at best only be rationalized. There are exceptions, e.g. documentaries

Whether someone likes a movie (or a song) is usually subjective, often emotional, and can at best only be rationalized. There are exceptions, e.g. documentaries. You could e.g. have the system recognize a preference for a director, actor, or genre, and add that to the predicted rating. But i don't think using that kind of information to make a prediction would add to a collaborative system's accuracy.