From STPA to Safe Behavior Models

Abstract

Model checking is a proven approach for checking whether the behavior model of a safety-critical system fulfills safety properties that are stated as LTL formulas.We propose rules for generating such LTL formulas automatically based on the result of the risk analysis technique System-Theoretic Process Analysis (STPA). Additionally, we propose a synthesis of a Safe Behavior Model from these generated LTL formulas. To also cover liveness properties in the model, we extend STPA with Desired Control Actions. We demonstrate our approach on an example system using SCCharts for the behavior model. The resulting model is not necessarily complete but provides a good foundation that already covers safety and liveness properties.