Hi Frank, thanks for your response.
The working method you described in your last paragraph does not seem to fit very well with our way of modelling in EA, though. Therefore, we still didn't find any good solution to our problem.
To put it simply, we are just trying to link an element to a diagram in EA in such a way that we can retrieve this link through the automation interface (indeed, our goal is not to be able to navigate this link interactively, just to retrieve it in the automation interface would be fine). As I explained earlier, the feature of making an element 'composite' is not a satisfactory solution for us, since this cannot be done for all elements (e.g. parts cannot be made composite).
What we already tried is dragging the diagram to which we want to link an element onto a diagram containing that specific element. We then chose "Add as diagram frame" in the dialog box, and just linked the element to the diagram frame by means of an association connector. Apart from the fact that this is a rather messy solution, there doesn't seem to be any way of retrieving the original diagram's Diagram ID from the diagram frame through the automation interface. Of course we can get the diagram's name from the frame, but in our projects these diagram names aren't unique. Besides, searching the EA repository for this name would be a heavyweight solution. So again, this does not seem to be a good solution...
Any further help would be greatly appreciated...