This diagram interchange metamodel allows diagrams to be represented with an additional semantic meaning by linking an element of an existing semantic model to a GraphElement via the abstract SemanticModelBridge. Each GraphElement has a link to a concrete subclass of SemanticModelBridge. If it is not a SimpleSemanticModelElement, it references the topmost super-class of the linked semantic model. For UML 1.x this is the class Element from the package Core, which is referenced by Uml1SemanticModelBridge. For UML 2.0 and later, this can be the class Element from the package Kernel, referenced by CoreSemanticModelBridge. This link allows the addition of UML-specific information to the graph. Other semantic models might be added as well, e.g., ER diagrams.
The model is designed to minimize the amount of redundant information. Due to this motivation, there is no extra attribute to indicate the semantic type of an element. In order to find out the semantic type of an element, the SemanticModelBridge must be examined. If the concrete subclass has a link to an element of the semantic model, all available semantic information about this element can be obtained.
Some elements allow more than one standard presentation. For example, an actor may be shown as a rectangle or as a stickman graphic. In order to distinguish these cases, the attribute 'presentation' defined in SemanticModelBridge indicates the desired presentation. This avoids the need to create complex DiagramElements such as Images to display standard elements.
To achieve the standard visualization of an element, presentation must be set to '', the empty string. For a non-standard treatment, it must be set to 'UserDefined'. This means that it is shown exactly as specified through the DiagramElements contained in the GraphElement associated with the Element. As most elements have exactly one standard presentation, Table 2 lists only those explicitly which have more than one. The others are collected under the term [Single Presentation].