A Mathematical Framework for Safecharts

Safecharts is a variant of Statecharts intended exclusively for safety critical systems design. Its specific features include an explicit representation of risks posed by different hazardous states, a separation of functional and safety concerns, a representation of component failures and characterisation of transitions based on the nature of their risk. This paper presents a rigorous mathematical framework for enabling greater clarity and accuracy in Safecharts. It contains a study of the representation chosen for risks and associated concepts such as risk graphs and safety oriented classification of transitions. The step semantics is also defined in relation to Safecharts. As lower level abstractions of states are brought into focus, a way of constructing risk graphs for and states is suggested. As a case study, the use of Safecharts in the domain of security is illustrated, in particular in modelling the Role-Based Access Control.

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