Composition of Safety Argument Patterns

Argument structure patterns can be used to represent classes of safety arguments. Such patterns can become quite complex, making use of loops and choices, posing a potential challenge for comprehension and evaluation, offsetting the likely gains that might follow from creating arguments using them. We show how complex patterns can be constructed by composition of simpler patterns. We provide a formal basis for pattern composition and show that this notion satisfies certain desirable properties. Furthermore, we show that it is always possible to construct complex patterns by omposition in this way. We motivate this work with example patterns extracted from real aviation safety cases, and illustrate the application of the theory on the same.