The study of the ?eld of user modeling (UM) has resulted in signi?cant amounts of theoretical work, as well as practical experience, in developing UM-based applications in traditional areas of human-computer interaction and tutoring systems. Further, it promises to have an enormous impact on recent developments in areas like information ?ltering, e-commerce, adaptive presentation techniques, and interface agents. A user model is an explicit representation of properties of a particular user, which allows the system to adapt diverse aspects of its performance to individual users needs....