Variability modules.

A Software Product Line (SPL) is a family of similar programs, called variants, generated from a common artifact base. A Multi SPL (MPL) is a set of interdependent SPLs: each variant can depend on variants from other SPLs. MPLs are challenging to model and to implement efficiently, especially when different variants of the same SPL must coexist and interoperate. We address this challenge by introducing the concept of a variability module (VM), a new language construct. A VM constitutes at the same time a module and an SPL of standard (variability-free), possibly interdependent, modules. Generating a variant of a VM triggers the generation of all variants required to satisfy its dependencies. Consequentially, a set of interdependent VMs represents an MPL that can be compiled into a set of standard modules. We illustrate the VM concept with an example from an industrial modeling scenario and formalize it in a core calculus. We define family-based analyses to check that a VM satisfies certain well-formedness conditions and whether all variants can be generated. Finally, we provide an implementation of VM for the Java-like modeling language ABS, and evaluate it with case studies.