Real-time Property Preservation in Approximations of Timed Systems

Formal techniques have been widely applied in the design of real-time systems and have significantly helped detect design errors by checking real-time properties of the model. However, a model is only an approximation of its realization in terms of the issuing time of events. Therefore, a real-time property verified in the model can not always be directly transferred to the realization. In this paper, both the model and the realization are viewed as sets of timed state sequences. In this context, we first investigate the real-time property preservation between two neighbouring timed state sequences (execution traces of timed systems), and then extend the results to two "neighbouring" timed systems. The study of real-time property preservation gives insight in building a formal link between real-time properties satisfied in the model and those in the realization

Predictable real-time software synthesis

Formal theories for real-time systems (such as timed process algebra, timed automata and timed petri nets) have gained great success in the modeling of concurrent timing behavior and in the analysis of real-time properties. However, due to the ineliminable timing differences between a model and its realization, synthesizing a software realization from a model in a predictable way is still a challenging research topic. In this article, we tackle this problem by solving a set of sub-problems. The solution is based on the theoretical results for property prediction proposed in Huang et al. (2003, Real-time property preservation in approximations of timed systems. In: Proceedings of 1st ACM and IEEE international conference on formal methods and models for codesign. IEEE Computer Society, Los Alamitos, pp 163---171) and Huang (2005, Predictability in real-time system design. PhD thesis, Eindhoven University of Technology, The Netherlands), where quantitative property relations are established between two absolute/relative close real-time systems. This theory basically implies that if two systems are close , they enjoy similar properties. These results cannot be directly applied in practice though, because a model and its realization typically have infinitely large absolute and relative timing differences. We show that this infinite time gap can be bridged through a sequence of carefully constructed intermediate time domains. Then the property-prediction results can be applied to any pair of adjacent time domains in the sequence. Consequently, real-time properties of the implementation can be predicted from the model. We propose two parameterized hypotheses to characterize the timing differences in the sequence and to guide a correctness-preserving design process. It is shown that these hypotheses can be incorporated in a concrete tool set. We demonstrate the feasibility of the predictable synthesis approach through the design of a railroad crossing system