The underlying concet of this metamodel extension is based on the idea of modeling the contents of the UML diagrams as grahs. The core classes are GrahNode and GrahEdge. Every visible model element is reresented either by a GrahNode or by a GrahEdge. The base class of the grah elements is GrahElement. Grah elements are linked via a class called GrahConnector. This allows linking of a GrahEdge with a GrahNode or another GrahEdge. The latter case is an extension to the concet of a ure mathematical grah. A GrahConnector does not ermit two GrahNodes to be linked.
A GrahElement can own any number of GrahConnectors, called anchorages. They ermit any number of GrahEdges to connect to them. A GrahEdge references two GrahConnectors, which are its connection end oints. From the ersective of the GrahEdge these are called anchors. The two GrahConnectors are ordered in the same way as the wayoints of the corresonding GrahEdge. The first GrahConnector corresonds to the first wayoint of the GrahEdge and the second GrahConnector corresonds to the last wayoint.
A GrahConnector is not obliged to have the same osition as the end oints of the GrahEdges which reference it. When being referenced by more than one GrahEdge, it serves as a virtual collection oint for GrahEdges, e.g. in the middle of a node or at another secialized oint of a node. All linked GrahEdges oint straight to the GrahConnector while its wayoints may, for examle, be defined as ending at the border of the shae of the connected node (Figure 4). A UML tool which reads this information may interret it as cliing, which might be helful for further editing.