Safety concepts are essential to conform to functional safety standard ISO 26262 for automotive products. Safety requirements, which are a part of safety concepts, shall be satisfied by products to avoid hazards by vehicles to maintain their safety. Incompleteness of safety requirements must be avoided in deriving parent requirements to its children. However, measure for checking is only reviewing when the safety requirements are described in a natural language. This measure for checking is not objective or stringent.
We developed a specification technique written in formal notation that addresses some of the shortcomings of capturing safety requirements for verification purposes. Safety requirements in this notation are expressed in goal tree models, which originate from goal-oriented requirement engineering Knowledge Acquisition in autOmated Specification (KAOS). Each requirement is written with propositional logic as the node of a tree. Completeness is automatically verified with a Boolean satisfiability (SAT) solver for each set of a parent goal and its children.
We found that the point of view to derive requirements was different between a natural language and the above formal specification. This leads to the difference in the hierarchical structure of requirements, and makes it difficult to convert them from one to the other. A method of supporting this conversion is proposed here as a solution by associating typical structures of requirements in a natural language and the formal specification. This solution is expected to strengthen the reliability of safety requirements by promoting the application of the formal specification technique.