Pattern Composition in Graph Transformation Rules

Graph transformation (GT) frequently serves as a precise underlying specification mechanism for model transformations within and between modeling languages. However, composability of graph transformation rules is typically limited to inter-level rule composition (i.e. rules calling other rules). In the current paper, we introduce intra-level composition for GT rules where the left-hand side and right-hand side graphs of GT rules can be composed of stand-alone graph patterns in a fully declarative way. As a result, the specification of complex model transformation problems can be drastically reduced. Our concepts are demonstrated using the transformation language of the VIATRA2 framework.