I don't know if I understand you correctly, but I think your are using the ClassDiagram demo
example of RadDiagram. And you want to add a connection (releation) between two shapes (classes). If so, you can do that by creating a new instance of ClassLinkViewModel and set its Target and Source properties to the objects of type ClassViewModel representing the classes you want to relate. Then add the ClassLinkViewModel object in the ClassDiagramGraphSource.
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