Distance Functions for Defaults in Reactive Systems
Default reasoning has become an important topic in software engineering. In particular, defaults can be used to revise specifications, to enhance reusability of existing systems, and to allow a more economic description of systems. In this paper we develop a framework for default specifications of reactive systems.
We present a formalisation of non-monotonicity in temporal logic based on the notion of default institution. Default institutions were defined as an extension of institutions in order to allow partial reuse of existing modules. The semantics of defaults is given by a (generalised) distance between interpretations. In this way, by defining a pre-order between temporal morphisms and using temporal logic as a specification language, we get a way of handling defaults in specifications of reactive systems. We illustrate the developed formalism with an example in which a specification is reused, but where the new behaviour contradicts the initial specification. In this example, the initial specification is seen as a default to which exceptions are added.
KeywordsTemporal Logic Linear Temporal Logic Nonmonotonic Reasoning Default Reasoning Proposition Letter
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