It is essential for user-adaptive systems to have information about the user. Without any user information an adaptive system is not able to adapt itself to the user's characteristics and preferences. The required information is stored and managed in form of user models. Thus, a user model represents the system's beliefs of the user. This work starts by giving the reader and overview of available and well-founded user modeling methods, standards and existing systems. This theoretical excursion into the field of adaptive user modeling systems allows us to come up with a new approach based on a service-oriented architecture. Service-oriented architecture with its main advantages of modularity and flexibility is and ideal candidate to implement as user modeling system as these are exactly the two main characteristics which we are looking for in such a systems. The technical part of this work compares several service-oriented frameworks and finally describes a service-oriented implementation of a user modeling system.