Specification and Verification of Real-time Embedded Systems using Time-constrained Reactive Automata

The vital role that real-time embedded systems are playing and will continue to play in our world, coupled with their increasingly complex and critical nature, demand a rigorous and systematic treatment that recognizes their unique requirements. The Time-constrained Reactive Automaton (TRA) is a formal model of computation that admits these requirements. Among its salient features is a fundamental notion of space and time that restricts the expressiveness of the model in a way that allows the specification of only reactive, spontaneous, and causal computations. Using the TRA formalism, there is no conceptual distinction between a system and a property; both are specified as formal objects. This reduces the verification process to that of establishing correspondences -- namely preservation and implementation relationships -- between such objects. In this paper, we present the TRA model and briefly overview our experience in using it in the specification and verification of real-time embedded systems

Requirements modelling of real-time systems

Real-time systems are characterised by the critical nature of their missions, and the demanding environment with which they interact. Real-time systems are used for dedicated applications. Every application is the subject of special requirements enforced by the customer. Considering the vital role that these systems play, it is imperative that a systematic approach be adopted in modelling their unique requirements. In this thesis I propose such a treatment. Real-time systems are time critical. Temporal requirements are the timing restrictions imposed by the application environment. Previous studies in requirements modelling of real-time systems have focused on adding the notion of time to modelling techniques of traditional systems without regard to the realities of requirements modelling. The information should be presented in the way the user handles it, and not the way which is convenient to the software engineer. I attempt to understand the needs of the users better by modelling the real world as close to the user's perspective as possible, and propose the Real World Model (RWM). RWM is assumed to be developed by users, and requirements engineers. An engineering approach to building the model is provided. A real-time system has a well defined use to its community. A requirements model must rely on the user level activities, and aid the human understanding and communication. In the RWM, a real-time system is viewed as a set of concurrently acting automata, each representing a system entity. This model supports temporal reasoning in easily described ways, for all classes of timing properties. A generalised classification of timing constraints is provided. A requirements modelling language facilitates the description of requirements, and serves as a medium of communication among developers and stakeholders. Jarke et al [Jarke 94] observe that there is a need for a requirements language that manages the relationship between the meta-level domain scheme, and the scenarios that actually instantiate the scheme under development. Here I propose Timed Requirements Language (TRL) to bridge this gulf between the world of stakeholders, and the world of specifiers. TRL has natural looking expressions for formulating the needs. TRL has a number of novel features including the treatment of causality, and the description of static, and dynamic constraints all integrated into one uniform framework. TRL has been used with a number of systems. The generality of the language is validated through its application to specific systems