Distributed Active Objects -- A Systemic Approach to Distributed Mobile Applications

Designing cyber-physical systems (CPS) requires consideration of interactions between several computing and non-computing elements and, thus, consideration of concurrency of actions. While concurrency alone is a complexity-introducing and error-prone concept, adding awareness of real time, real space and/or mobility makes things worse: It prohibits to utilize common abstractions, which are usually used in distributed system design to reach transparency. In this paper, we present a concept to achieve a systemic description of location- and motion-aware applications and to make concurrency implicit while guaranteeing location, distribution and motion transparency with respect to the executing system or rather its components. We are doing so by providing a programming and an execution model. The former provides means to separate imperative functional program code and declarative spatio-temporal aspects at application level and, thus, allowing for systemic descriptions of applications. The latter executes the application in a distributed fashion, avoiding explicit communication. We describe our models, present a run-time system and the supporting tool chain, and demonstrate the application of our concept with a simple example.