After a thorough analysis of the specific "Enterprise Archtitect"-specific API (Automation Interface - AI) the following tool-data specific metamodel could be deduced. It represents a subset of the basic functionality so far.
Enterprise Architect provides a COM-based Automation Interface. Connect to this Automation Interface, we use JACOB an opensource Java to COM bridge, that enables an easy to use reflective method call from Java to COM interfaces. The following picture shows an architecural overview of the communication layer of the adapter.