Hierarchical Behavior Annex: Towards an AADL Functional Specification Extension

AADL is a modeling language to design and analyze embedded real-time systems and is widely used to model safety-critical systems. AADL describes the system models hierarchically through components such as systems, processes, and threads, etc. The Behavioral Annex is a supplement of AADL in terms of functional behavior. It enables modeling component and component interaction behavior in a state-machine-based annex sublanguage. At present, there is no mechanism to represent hierarchical automata in the behavioral annex. However, this is a very important feature because industrial complex systems are always described with concurrent and composite states. Although we can model a system with AADL's own hierarchical description capabilities, it will result in a large amount of threads. In actual development, a refinement process is always needed before system synthesis, in which several threads may be combined into one thread that has concurrent and composite states. This paper proposes a hierarchical extension of the AADL behavioral annex which is named HBA (Hierarchical Behavior Annex). First, the formal syntax of HBA is given, and then we formally define the semantics of HBA. We propose a meta-model of HBA and implement its textual and graphical editor in the OSATE environment. Finally, an industrial case study is given to validate the approach.