The references to model elements are made using a notation that looks like XPath but I want to use the xmi:id attribute.
I can generate them inside of eclipse by checking the "Output model content types detection" setting as shown by the following excerpt:
However, I cannot find how to trigger this behaviour from an external program as setting the option "OPTION_CONTENT_TYPE" to true in the options of the launcher does not help.
Is there anyone here who might have an idea on how these xmi:id are generated ?
This isn't an ATL problem.
For serialization, ATL delegates to the corresponding resource factory.
This is done using the file extension.
Try to save the output file as a ".uml" file, this should give you what you want.