We are looking for a formal notation or language for megamodels preferably with a graphical representation (but text will do). To my knowledge, beside the basics defined by Favre, there does not exist one commonly used notation. We need to describe models, meta-models, transformations, and transformations as source and target models.
Thanks for your help
Reiner
It could be useful to look at AADL (http://www.aadl.info/aadl/currentsite/), SysML (http://sysml.org/).
A Formal Language widely used is the Z notation, mainly because of its ease of application, the modularization (which lets you specify any system size) and ease of understanding.
I found "Towards a Basic Theory to Model Model Driven Engineering" which discusses different ways to define a basic theory on megamodels based on Z and alternatively in Prolog and other notations. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.202.2109&rep=rep1&type=pdf
You can use object-role modeling (ORM) to design large models. ORM is a graphical language that is based on first order logic and set theory. ORM has been implemented in a free tool called NORMA which you can download from https://www.ormfoundation.org/files/folders/norma_the_software/default.aspx