Version control in the Inscape environment

We present the important issues to be considered in version control mechanisms and characterize and compare the kinds of version control systems extant in current programming environments. We then characterize Inscape's version control mechanism. Invariant, and show that it makes several significant advances in the state of the art. Using Instress (Inscape's module interface specification language) specifications, Invariant provides a better understanding of the notion of parallel versions, a more comprehensive notion of version consistency, and a more flexible method of system composition than current mechanisms. In particular, Invariant provides a formalization of the notions of version equivalence and compatibility that correspond closely with our intuitive (and practical) notions of version equivalence and compatibility. These various forms of version compatibility provide the system builder with the concept of plug-compatibility — an extremely useful facility in composing systems from component parts.