Variability Models Must Not be Invariant!

Variability modeling techniques are used to specify variable aspects of members of a family of related software artifacts. Instances of variability models are then used to efficiently produce members of such a family. By making variability explicit, variability models determine implicitly the common properties among family members as well. This partitioning of information into variable and invariant parts predetermines the reuse benefit obtainable from a variability model. In most current approaches to variability modeling, the decision between variable and invariant information has to be done in an up-front manner and is very difficult to change later on. However, the distinction between variable and common parts of members of a system family varies over time. Variability modeling techniques must thus be able to cope with changes to the variability