An Ontology-Based Approach to Aid STPA Analysis

The safety-critical systems we are building today employ software, use physical and cybernetic components, and have more interactions (including hierarchical controllers). Systems-Theoretic Process Analysis (STPA) is a hazard analysis method that is used in the concept stage of the safety-critical systems life-cycle. It is claimed that STPA identifies more loss scenarios and safety recommendations when compared to traditional safety analysis methods. However, the STPA analyses are lengthy and complex, and it is common to miss some loss scenarios and safety recommendations. Few STPA-based tools allow systematic and automated analyses. We propose an ontology that represents the STPA analysis domain knowledge and we built an STPA ontology-based tool, called AppSTPA, that aids the analyst providing a more systematic, automated and guided analyses. We evaluated the STPA analyses made with AppSTPA and without the assistance of tools. We also assessed the benefits of AppSTPA when compared to an existing STPA tool. The results show that our ontology-based tool provides pertinent guidance and allows a more complete analysis. We conclude that our STPA ontology-based tool is able to support analysts and provide valuable suggestions, resulting in better safety analyses.