Extending Safety Deviation Analysis Techniques to Elicit Flexible Dependability Requirements

In mission critical systems the operational success of the system depends on many aspects of the system’s operation such as availability, security, performance and safety. According to the design of the system, dependability attributes can be in conflict or in harmony often resulting in unavoidable trade-offs. Adopting a more flexible approach towards dependability allows us to achieve tolerable limits for each dependability attribute, whilst maintaining acceptable overall dependability levels for the system. Elicitation of the requirements that define the levels of the dependability attributes can only be meaningfully done in the context of the system’s operation. In this paper we present how we can extend existing safety techniques to elicit dependability requirements. Well established deviation analysis techniques in the safety domain are already used to perform safety analysis. However the safety techniques cannot be used efficiently to explicitly elicit requirements for other attributes. This is primarily because the prompts as well as the models on which the prompts are applied are optimised for safety. The method presented uses a set of prompts optimised to examine the system for dependability attribute concerns, which are applied on models, taken from the MOD architectural framework, that are suitable for analysing each of the dependability attributes.