Version control systems are an integral part of today's software and systems development processes. They facilitate the management of revisions (sequential versions) and variants (concurrent versions) of a system under development and enable collaboration between developers.
Revisions are commonly maintained either per file or for the whole system. Variants are supported via branching or forking mechanisms that conceptually clone the whole system under development.
It is known that such cloning practices come with disadvantages.
In fact, while short-lived branches for isolated development of new functionality (a.k.a. feature branches) are well supported, dealing with long-term and fine-grained system variants currently requires employing additional mechanisms, such as preprocessors, build systems or custom configuration tools.
Interestingly, the literature describes a number of variation control systems, which provide a richer set of capabilities for handling fine-grained system variants compared to the version control systems widely used today.
In this paper we present a classification and comparison of selected variation control systems to get an understanding of their capabilities and the advantages they can offer. We discuss problems of variation control systems, which may explain their comparably low popularity. We also propose research activities we regard as important to change this situation.