State Identification for Labeled Transition Systems with Inputs and Outputs

Abstract

Various relations have been defined to express refinement and conformance for state-transition systems with inputs and outputs, such as ioco and uioco in the area of model-based testing, and alternating simulation and alternating-trace containment originating from game theory and formal verification. Several papers have compared these independently developed relations, but these comparisons make assumptions (e.g., input-enabledness), pose restrictions (e.g., determinism - then they all coincide), use different models (e.g., interface automata and Kripke structures), or do not deal with the concept of quiescence. In this paper, we present the integration of the ioco/uioco theory of model-based testing and the theory of alternating refinements, within the domain of non-deterministic, non-input-enabled interface automata. A standing conjecture is that ioco and alternating-trace containment coincide. Our main result is that this conjecture does not hold, but that uioco coincides with a variant of alternating-trace containment, for image finite interface automata and with explicit treatment of quiescence. From the comparison between ioco theory and alternating refinements, we conclude that ioco and the original relation of alternating-trace containment are too strong for realistic black-box scenarios. We present a refinement relation which can express both uioco and refinement in game theory, while being simpler and having a clearer observational interpretation.