Designing information hiding modularity for model transformation languages

Development and maintenance of model transformations make up a substantial share of the lifecycle costs of software products that rely on model-driven techniques. In particular large and heterogeneous models lead to poorly understandable transformation code due to missing language concepts to master complexity. At the present time, there exists no module concept for model transformation languages that allows programmers to control information hiding and strictly declare model and code dependencies at module interfaces. Yet only then can we break down transformation logic into smaller parts, so that each part owns a clear interface for separating concerns. In this paper, we propose a module concept suitable for model transformation engineering. We formalize our concept based on cQVTom, a compact subset of the transformation language QVT-Operational. To meet the special demands of transformations, module interfaces give control over both model and code accessibility. We also implemented the approach for validation. In a case study, we examined the effort required to carry out two typical maintenance tasks on a real-world transformation. We are able to attest a significant reduction of effort, thereby demonstrating the practical effects of a thorough interface concept on the maintainability of model transformations.