To connect or not to connect: experiences from modeling topological variability

Variability management aims at taming variability in large and complex software product lines. To efficiently manage variability, it has to be modeled using formal representations, such as feature or decision models. Such models are efficient in many domains, where variability is about switching on and off features, or using parameters to customize products of the product line. However, variability can be represented in the form of a topology in domains where variability is about connecting components in a certain order, in specific interconnected hierarchies, or in different quantities. In this experience report, we explore topological variability within a case study of large-scale fire alarm systems. We identify core characteristics of the variability, derive modeling requirements, model the variability using UML2 class diagrams, and discuss the applicability of further variability modeling languages. We show that, although challenging, class diagrams can suffice to represent topological variability in order to generate a configurator tool. In contrast, modeling parallel and recursive structures, cycles, informal constraints, and orthogonal hierarchies were among the main experienced challenges that require further research.