Safe evolution of product populations and multi product lines

A product line is often developed in the context of a set of related product lines. When supporting separate feature development, we might have product populations, with product line versions being simultaneously developed in different branches. Multi product lines involve a number of product lines that depend on each other. A product line refinement notion formalizes safe evolution, but this is not sufficient for reasoning over sets of product lines. We propose refinement notions and compositionality properties that help to explain how we can support modular development in these contexts. Thus, we formally define the foundations for safe and modular evolution of product populations and multi product lines, enabling developers to perform changes in a systematic manner.