Back to the future

A Software Product Line (SPL) captures families of software products and its functionality is captured as features in a feature model. Similar to other software systems, SPLs and their feature models are subject to evolution. Temporal Feature Models (TFMs) are an extension to feature models that allow for engineers to model past feature-model evolution and plan future evolution. When planning future evolution of feature models, multiple evolution steps may be planned upfront but changed requirements may lead to retroactively introducing evolution steps into the planned evolution or changing already planned steps. As a consequence, inconsistencies, which we denote as evolution paradoxes, may arise leading to invalidity of already modeled future evolution steps. In this paper, we present first steps towards allowing to introduce intermediate evolution steps into planned evolution while preserving consistency of all future evolution steps. To this end, we outline a method to define and check model evolution consistency rules. Using this method, engineers are allowed to introduce intermediate feature-model evolution steps whenever these changes preserve the evolution consistency rules.