A case study for evaluating bidirectional transformations in QVT relations

In model-driven software engineering, high-level models of a software system are eventually transformed into executable code. Model transformations constitute a key technology for model-driven software engineering. QVT Relations (QVT-R) is a language for the declarative specification of model transformations which was defined in an OMG (Object Management Group) standard. In addition to unidirectional transformations, QVT-R supports bidirectional transformations: Rather than writing two unidirectional transformations separately, the user may provide a single relational specification which may be executed in both directions. In this way, the specification of a bidirectional transformation may be simplified considerably - which is crucial e.g. for round-trip engineering. This paper investigates a case study for evaluating QVT-R's capabilities for specifying bidirectional transformations. Even in this rather simple case study, development of a bidirectional transformation turns out to be more complex than expected. Motivated by the case study, we propose extensions to QVT-R which facilitate the specification of bidirectional transformations considerably.