STAIRS: Steps to analyze interactions with refinement semantics

Abstract. The paper presents STAIRS, an approach to the compositional de-velopment of UML interactions supporting the specification of mandatory as well as potential behavior. STAIRS has been designed to facilitate the use of interactions for requirement capture as well as test specification. STAIRS as-signs a precise interpretation to the various steps in incremental system devel-opment based on an approach to refinement known from the field of formal methods, and provides thereby a foundation for compositional analysis. An in-teraction may characterize three main kinds of traces. A trace may be (1) posi-tive in the sense that it is valid, legal or desirable, (2) negative meaning that it is invalid, illegal or undesirable, or (3) considered irrelevant for the interaction in question. This categorization corresponds well with that of testing where the verdict of a test execution is either pass, fail or inconclusive. The basic incre-ments in system development are structured into three kinds referred to as sup-plementing, narrowing and detailing. Supplementing categorizes inconclusive traces as either positive or negative. Narrowing reduces the set of positive traces to capture new design decisions or to match the problem more adequately. De-tailing involves introducing a more detailed description without significantly altering the externally observable behavior.