Generic user modeling systems

The paper reviews the development of generic user modeling systems over the past twenty years. It describes their purposes, their services within user -adaptive systems, and the different design requirements for research proto types and commercially deployed servers. It discusses the architectures tha t have been explored so far, namely shell systems that form part of the app lication, central server systems that communicate with several applications , and possible future user modeling agents that physically follow the user. Several implemented research prototypes and commercial systems are briefly described.