A method for establishing integrity in software-based systems

In this paper, the authors present a digital system requirements specification method that has demonstrated a potential for improving the completeness of requirements while reducing ambiguity. It assists with making proper digital system design decisions, including the defense against specific digital system failures modes. It also helps define the technical rationale for all of the component and interface requirements. This approach is a procedural method that abstracts key features that are expanded in a partitioning that identifies and characterizes hazards and safety system function requirements. The key system features are subjected to a hierarchy that progressively defines their detailed characteristics and components. This process produces a set of requirements specifications for the system and all of its components. Based on application to nuclear power plants, the approach described here uses two ordered domains: plant safety followed by safety system integrity. Plant safety refers to those systems defined to meet the safety goals for the protection of the public. Safety system integrity refers to systems defined to ensure that the system can meet the safety goals. Within each domain, a systematic process is used to identify hazards and define the corresponding means of defense and mitigation. In both domains, the approach and structure are focused on the completeness of information and eliminating ambiguities in the generation of safety system requirements that will achieve the plant safety goals