Fault-Free Refinements for Interface Automata

Abstract

A refinement preorder for a model of concurrent systems should be compositional (i.e. a precongruence for parallel composition) and should not introduce faults into a fault-free specification. Arguably, if these are the features of interest, the coarsest such precongruence is the optimal refinement preorder and often, it preserves additional properties. For the model of interface automata, originally faults are communication errors in the form of unexpected inputs. The respective optimal preorder has been characterized as the inclusion of two trace sets. Here, we extend these characterizations by regarding also quiescence (quiescence and divergence resp.) as faults. The latter preorder is coarser, i.e. better, than an earlier preorder regarding errors, quiescence and divergence. A conjunction operator allows to specify different facets of an overall specification by separate automata and then to combine them. We also present conjunction operators for our settings, avoiding flaws that can be found in the literature.