The things you place on a diagram, may be used to create a model element if it does not already exist but they ultimately are just representations of the model element. Multiple diagrams may contain the same element, show different aspects or detail of the same diagram element. They are the same model element, which you can show by changing some property of the underlying model element; all the diagrams will change to reflect the new reality (see Fig. 2.3). In fact, the same element can appear multiple times on the same diagram or on multiple diagrams.