Eliminating Crosscutting Constraints from Visual Model Transformation Rules

This paper presents the aspect-oriented constraint management of the Visual Control Flow Language (VCFL) applied in the Visual Modeling and Transformation System (VMTS). To define the transformation steps precisely, additional constraints must be specified beyond the structure of the visual models (such as UML models). Structural and attribute transformation methods cannot perform and express the issues, which can be addressed by constraint validation. The use of OCL as a constraint and query language in modeling is a suitable choice. In our experience, constraints are proven to be useful in model transformations as well: VCFL uses OCL constraints to define constraints on the nodes of the transformation steps and to choose between different control flow branches. Often, the same constraint is repetitiously applied in many different places in a transformation and crosscuts it. It would be beneficial to describe a common constraint in a modular manner and designate the places where it will be applied. Using an illustrative case study, this paper introduces the problem of crosscutting constraints in visual model transformation steps, and provides an aspect-oriented solution for it, applying aspectoriented constraints and constraint weaving methods. Finally, the similarities between AOP and the AO constraint concepts are also discussed.