Managing Complex Safety Cases

Safety case reports are often complex documents presenting complex arguments. To manage the complexity of safety case construction, system safety cases are often decomposed into subsystem safety cases. In this paper we discuss the motivation and problems of partitioning the safety case, both as practiced historically, and as required in new modular, reconfigurable systems such as Integrated Modular Avionics. Recent work on managing safety cases “in-the-large” is presented. In particular, we demonstrate how notions of software and systems architecture design can be read-across to establish the concepts of “safety case architecture” and contract based reasoning for managing inter-safety case dependency. Problems of division of responsibility in safety case development will also be discussed.