Transformations between models

 Hi Martin ,
 Is there a way to convert an UML meta-model to a different meta-model that
I wrote?  (My meta-model is an extension of the UML one)
 I'd like to define some transformation rules that are read (and applied)
by a transformation engine.
 I'm looking for tools, libraries or languages that do this. Do they exist?
 I tried using XSLT stylesheets for my transformations, but it turns out
that doing complex operations this way is very hard

 Regards
 Gabriele