SHIP: Research supporting the Safety Case Approach

In SHIP, we have examined the general approach to constructing a safety case and examined specific safety cases to see how the argument is constructed and what evidence is employed. In this area we have examined:

• methods for combining evidence
• alternative argument inference mechanisms (deterministic, probabilistic and qualitative)

In addition, we have undertaken research on specific types of evidence and arguments that can be deployed in .safety case reliability assessments, namely:

• fault quantification from the development process and product measures
• the use of diversity for failure containment
• reliability estimation from dynamic testing
• reliability estimation using reliability growth modelling

Case study examples utilising some of these techniques are referenced in supporting technical papers, and some selected examples are presented in later sections.

It can be seen that the reliability grows with operational use, and it was also shown that growth was better for less complex systems. This is consistent with the PLC study results which indicated that faults are eliminated more rapidly in simple designs.