Requirements modeling for real-time software development

The requirements modeling techniques that were successfully applied to the development of a facility to perform software development and integration testing of aircraft embedded software are described. This facility mimics the dynamic environment experienced by the software executing within actual avionics hardware. The requirements for each software component in the system are modeled from three perspectives: processing, information, and behavior. The process view treats the system as a planned response system. Events that require a system response are identified and assigned a process. Processes are decomposed to minimize interfaces, and are grouped to preserve the stimulus-response structure. The information view identifies data retained by the system and the system interfaces. Retained data attributes are defined in entity relationship diagrams. Interfaces between components are identified by grouping data into data structures. The behavioral view identifies system modes of operation and control. State transition diagrams are used to identify each system state and the events in which transitions occur. The behavioral view is linked to the process model by control specifications. Application of this approach improves communication to development groups by reducing complexity. It is amenable to both functional and object-oriented design approaches