[news.eclipse.modeling.gmf] How I can add graphical elements to my file

[bricelaurel@xxxxxxxxx (Brice Laurel)]

Hi list,

I read and do this tutorial 
http://wiki.eclipse.org/index.php/GMF_Tutorial. I have the figure with 3 
topics :
  - a topic ;
  - a subtopic ;
  - another subtopic.
Now, I want to add another topic in my figure programmatically.
I create a plugin's project that allow me to add a figure to file 
"default.mindmap_diagram" programmatically. 
I think I can use the code
 MindMapFactory.eINSTANCE.create(Topic); am I wrong?
I don't see when the link between this instruction with file 
"default.mindmap_diagram"?

Thanks in advance for your help.