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An interactive component consumes a stream of input messages and produces a stream of output messages. The input/output behaviour describes the service offered by the component without disclosing the implementation. In general, an interactive component provides the contracted service only for a subset of input histories, called its service domain. We investigate the input/output behaviour of interactive components for erroneous input streams outside the service domain. We specify a fault sensitive behaviour, a fault tolerant behaviour, a robust behaviour, and a fault correcting behaviour by enlarging the regular behaviour in a systematic way. We implement the different behaviours by state transition machines where we enlarge the regular state space by additional information. Altogether we provide schematic transformations both on the specification and on the implementation level how to extend the regular behaviour of an interactive component to input streams outside the service domain. The resulting formal method separates the aspects of service provision and error handling in an orthogonal way. |
