As one of the initial tasks of the project, we have developed a small interpreted toy executable Domain-Specific Model Modeling Language (xDSML), more precisely a Domain-Specific Transformation Language (DSTL), called MiniTL.
The language defines a model transformation as a set of rules, each with an input and an output object template.
We implemented the language (including its operational semantics) in the GEMOC Studio using Ecore, Xtext, Kermeta 3 and Melange. You can find much more detailed information on the Github repository of MiniTL!
MiniTL toy example on GitHub