Supporting location-awareness in open distributed systems

Mobile computers and communication devices are establishing themselves as ubiquitous features of daily life. This development is linked to tremendous growth in the number and sophistication of mobile and mobile-aware software applications. Increasingly, such applications need access to information about their own and other objects' physical locations, a requirement known as location-awareness. Existing location-aware applications and systems are typically tailored to a particular type of positioning technology. This is unsatisfactory considering that no technology provides ubiquitous coverage. Equally, there are few accepted models and abstractions for building location-aware applications, making their design and implementation costly and error-prone. Location-awareness raises legitimate concerns about personal and organisational privacy. These vary widely across administrative and application domains. Hence, there is a need to nd a model allowing a balance between protection and functionality as appropriate for a particular target environment. The functionality and structure of a location-aware system fundamentally depends on the location model employed. In this thesis, we argue that a formally speci ed location model facilitates design and implementation of such systems. Also, location-awareness generally cannot be achieved autonomously but requires support by a location service, tracking physical location of objects, and optionally providing location prediction, access control and other functions. Inevitably, location service and location model are closely intertwined. This work presents a model of location information, the components of a location service to support it, and an architecture-independent protection model. Our approach is characterised by the following orthogonal principles: A global, general location service provides a ubiquitous infra-structure for locationaware applications, A hierarchical, semi-symbolic location model forms the basis of the service's functionality and structure, Location privacy is protected by policy-based access control. The applicability of the model is supported by an implementation of a general location service prototype.