Improving Model Usability and Utility by Layered Diagrams

Background: Large and complex diagrams are hard to understand, yet sometimes unavoidable. In other disciplines, diagrams are routinely organized into layers to tackle complexity–why not in Software Engineering? Objective: We want to understand whether layered diagrams are a useful addition to the software engineers repertoire. If so, how are layers best used, and what features and properties should they have? Method: First, we explore the design space. We study how layers are used in other disciplines, discuss sample layered diagrams, and derive design decisions. We implement layered diagrams in an experimental modeling tool, and provide an initial validation, exploring the usage space in a field study. Results: Layers are intuitive to use and benefit many usage scenarios that are poorly supported by most contemporary tools. Conclusions: Layered diagrams complement conventional diagrams and model structuring techniques. They are easy to comprehend and apply by modelers, and allow richer models. With layered diagrams, the utility and usability of existing modeling tools can be improved at little cost.