Perspicuity and Granularity in Refinement

This paper discusses how different ways of introducing “extra” actions in refinement (such as weak refinement, action refinement, stuttering steps) relate to the underlying refinement relations used (e.g. trace refinement, failures refinement). In particular, we aim to show how the choices in those two dimensions are interdependent. The paper is not intended to be polemic (“my formalism/refinement relation is better than yours”) nor is it really meant to be a first introduction to the topic. Where it appears to state the obvious, this is in an attempt to ensure that commonalities, differences, and design decisions in refinement relations are exhibited in an unambiguous and uncontroversial way.