In the UModel API, graphical objects on diagrams are represented by objects derived from the IUMLGuiElement interface. Most of them can be accessed using the IUMLGuiDiagram property 'GuiLinks'.
For most diagrams, most objects which are lines are instances of IUMLGuiLineLink and most other, solid objects or 'nodes' are instances of IUMLGuiNodeLink. These interfaces have properties and methods for manipulating the basic properties of these graphical objects, such as position, color and style.
There are of course more specialized interfaces derived from these general interfaces which provide access to special properties. The following image shows a sequence diagram and the interface representing each graphical object on it: