Modelling and analysing contextual failures for dependability requirements

The notion of Contextual Requirements refers to the inter- relation between the requirements of a system, both functional and non-functional (NFRs), and the dynamic environ- ment in which the system operates. Dependability requirements are NFRs which could also be context-dependent. The meaning and the consequence of faults affecting dependability vary in relation to the context in which a fault occurs. In this paper, we elaborate on the need to consider the contextual nature of failures and dependability. Then, we extend a contextual requirements model, the contextual goal model, to capture contextual failures and utilize that to enrich the semantic of dependability requirements. We provide techniques to analyse and reason about the effects of contexts on failures and their consequences. This analysis helps evaluate the possible alternative configurations to reach goals from dependability perspective and, hence, take adaptation decisions. Finally, we demonstrate the feasibility and applicability of our approach on a Mobile Personal Emergency Response system.