Sequential Constructiveness, SCCharts for Safety-Critical Applications

We present a new visual language, SCCharts, designed for the model-driven engineering of safety-critical reactive systems. SCCharts provide determinate concurrency based on a synchronous model of computation (MoC), without restrictions common to previous synchronous MoCs. SCCharts [vHDM14] use a statechart notation [Har87] and provide determinate concurrency, based on a synchronous model of computation (MoC) [And04]. We lift earlier limitations on sequential accesses to shared variables, by leveraging the sequentially constructive (SC) MoC [vHMA14, AMvHF14]. In essence, the SC MoC extends the classical synchronous MoC by allowing variables to be read and written arbitrarily as long as sequentiality expressed in the program provides sufficient scheduling information to exclude race conditions. Previous approaches have excluded test-then-set code such as “if (! initialized) { init(); initialized = true; }” because it requires a write after a read. The SC MoC permits a compiler to safely admit such statements. The semantics and key features of SCCharts are defined by a very small set of language elements, the Core SCCharts, consisting of state machines plus fork/join concurrency. Conversely, Extended SCCharts contain a rich set of advanced features, such as different abort types, signals, history transitions, etc., as illustrated in Fig. 1; all of these can be reduced via model-to-model transformations into Core SCCharts [MSvH14]. This approach enables a simple yet efficient compilation strategy and aids verification and certification. An open-source, class-room tested SCChart editor/compiler is available in the Eclipse-based modeling framework KIELER. ∗This work was supported by the German Science Foundation (DFG HA 4407/6-1 and ME 1427/6-1) as part of the PRETSY project. http://www.informatik.uni-kiel.de/rtsys/kieler/