Zooming-out on Higraph-based diagrams

Computing system representations based on Harel's notion of hierarchical graph, or higraph, have become popular since the invention of Statecharts. Such hierarchical representations support a useful filtering operation, called “previous termzoomingnext term-out”, which is used to manage the level of detail presented to the user designing or reasoning about a large and complex system. In the framework of (lightweight) category theory, we develop the mathematics of previous termzooming e ut for higraphs with loose edges, formalise the transition semantics of such higraphs and conduct an analysis of the effect the operation of previous termzooming out has on the semantic interpretations, as required for the soundness of reasoning arguments depending on zoom-out steps.