In this paper we motivate the importance of the field of mobile computing and survey current practical and formal approaches. We argue that existing formalisms are not sufficiently general and powerful because they do not model all necessary concepts of mobility adequately. The main contribution of the paper is therefore, to identify and define the fundamental concepts of mobile systems by providing a precise, mathematical foundation. The model we present is an extended variant of existing, compositional network models for control and data flow of non-mobile systems, enriched by the concept of locations as places containing components. To model the migration of a component from one location to another, the containment relation may change dynamically over time. Based on this formal model, we define a number of fundamental properties and characteristics such as network transparency. Finally, we demonstrate how existing description techniques may be extended in the context of mobility, and sketch a supporting case tool.
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