On fault tolerance reuse during refinement

Complex modern applications have to be developed to be dependable to meet their requirements and expectations of their users. An important part of this is their ability to deal with various threats (such as faults in the system environment, operator's mistakes, underlying hardware and software support problems). Development of modern applications is complicated by the need for systematic and rigorous integration of fault tolerance measures. The paper focuses on reuse of fault tolerance modelling. First, it introduces the idea of general modelling templates reflecting abstract views on system behaviour with respect to faults. These templates are used during system detalisation (refinement) to capture the user's view on system external behaviour. Secondly, it proposes to use a library of concrete modelling patterns allowing developers to systematically integrate specific fault tolerance mechanisms (e.g. recovery blocks, checkpoints, exception handling) into the models. The proposed solutions are linked to the Event-B method and demonstrated using a case study.