Enhancing the Maintainability of Safety Cases Using Safety Contracts

Abstract: Safety critical systems are those systems whose failure could result in loss of life, significant property damage, or damage to the environment. These systems require high quality and dependability levels in them, where system safety is a major property that should be adequately assured to avoid any severe outcomes. Many safety critical systems in different domains (e.g., avionics, railway, automotive, etc.) are subject to a certification. The certification process is based on an evaluation of whether the associated hazards to a system are mitigated to an acceptable level. Safety cases are often required to demonstrate how a regulatory body can reasonably conclude that a system is acceptably safe from the evidence available. The development of safety cases has become common practice in many safety critical system domains. However, safety cases are costly since they need significant amount of time and efforts to produce. This cost can be dramatically increased (even for already certified systems) due to system changes as they require maintaining the safety case before it can be submitted for certification. Anticipating potential changes is useful since it reveals traceable consequences that will eventually reduce the maintenance efforts. However, considering a complete list of anticipated changes is difficult. What can be easier though is to determine the flexibility of system components to changes.Sensitivity analysis has been proposed as a useful tool to measure the flexibility of the different system properties to changes. Furthermore, the concept of contracts have been proposed as a means for facilitating the change management process due to their ability to record the dependencies among system's components. In this thesis, we use sensitivity analysis to support changes prediction and prioritisation. We also use safety contracts to record the information of changes that will ultimately advise the engineers what to consider and check when changes actually happen.