A Two-level Calculus for Composing Hybrid QVT Transformations

Abstract

The standard for model transformations QVT offers two dialects: Relations Language and
Operational Mappings Language. Each one of these dialects can be used in isolation, resulting in
purely declarative transformations or purely imperative transformation respectively; alternatively, both
dialects can be combined resulting in a hybrid transformation approach. On the other hand, the
availability of compositional approaches to produce complex transformations from smaller units is a
major concern in the area of model transformations. Compositional approaches for pure QVT
transformations are supported by a number of tools; however no composition technique exists that can
consistently manage the hybrid approach. Such partial techniques provide suitable answers to most
practical needs; but they do not cover the entire composition spectrum. The aim of this article is to
describe a technique for composing model transformations embracing both dimensions - declarative
and imperative - so that the hybrid approach can be smoothly supported. Additionally, we report the
implementation of a software tool supporting such technique and we sketch its validation.