Safety-critical systems (SCSs) have become an intrinsic part of human dailylife in multiple domains, such as automotive, avionics, and rail industries. Such systems are not only required to implement the functionality they should provide, but also have to satisfy a set of safety requirements in order to ensure the mitigation of hazardous consequences.
It is fundamental that safety requirements are defined based on the results issued from safety analysis. Various studies have asserted that most significant flaws in the safety requirements are related to the omission of hazards and causes associated with the identified hazards in early stages of SCSs development. The main drawbacks of the current practice applied in safety analysis,lie in that:
• due to the lack of a common understanding of the hazard concept, the hazards and their causes are typically identified in accordance to the intuition and experience of the analysts and,
• analysts are inclined to identify generic causes for a certain hazard description, for example, “Design flaw, Coding error, and Human error”and,
• there is an essential need to formalize the experience of the analysts in a structured way, in order to save effort and,
• since traditional safety analysis techniques are usually based on well known system behaviors represented by models, such as automata and sequence diagrams, a new approach is needed when such behavioral models are not available.
These considerations motivate us to formulate the following general research question: How can safety analysis, within the context of safety-critical systems, be conducted to reduce the omission of potential hazards and their causes in early stages of the system development life-cycle?
In this thesis, we propose an ontological approach to safety analysis for safety-critical systems, which mainly consists of four pieces of work:
• we propose an ontological interpretation of the hazard concept, calledthe Hazard Ontology (HO), to define an explicit representation of theknowledge of hazards and their relations with the system under analysisand existing environment and,
• we propose an approach to identify hazards in early stages of thesafety-critical systems development, based on the HO and,
• we propose an approach to identify the causes associated with a certain hazard description for safety-critical systems, based on the HO and,
• we propose a heuristic approach to safety requirements elicitation,based on the HO.