Connecting software build with maintaining consistency between models: towards sound, optimal, and flexible building from megamodels

Software build systems tackle the problem of building software from sources in a way which is sound (when a build completes successfully, the relations between the generated and source files are as specified) and optimal (only genuinely required rebuilding steps are done). In this paper, we explain and exploit the connection between software build and the megamodel consistency problem. The model-driven development of systems involves multiple models, metamodels and transformations. Transformations—which may be bidirectional—specify, and provide means to enforce, desired “consistency” relationships between models. We can describe the whole configuration using a megamodel. As development proceeds, and various models are modified, we need to be able to restore consistency in the megamodel, so that the consequences of decisions first recorded in one model are appropriately reflected in the others. At the same time, we need to minimise the amount of recomputation needed; in particular, we would like to avoid reapplying a transformation when no relevant changes have occurred in the models it relates. The megamodel consistency problem requires flexibility beyond what is found in conventional software build, because different results are obtained depending on which models are allowed to be modified and on the order and direction of transformation application. In this paper, we propose using an orientation model to make important choices explicit. We show how to extend the formalised build system pluto to provide a means of restoring consistency in a megamodel, that is, in appropriate senses, flexible, sound and optimal.