An integrated and federated location service

With the advent of mobile computing devices and cheap location sensing systems, location information has become an important resource both for mobile and `desktop´ users. We describe some key concepts a scalable ubiquitous location service should be based on. Firstly, we show how such a service can accommodate multiple location sensing systems. Secondly, we discuss hierarchy-based access control policies as flexible and powerful mechanisms to protect users´ privacy. Thirdly, we describe server federation as a means to incrementally build a global location service