A link component shows the relationship between two symbols. It needs to define connections between itself and other components. Accordingly, it is derived from CODSymbolComponent so it has the connection logic.
A link comprises of a line component and two port components. The ports are set at either end of the line. They are always ready to connect to another symbol. Normally, a composite component like this would have eight selection handles instead of control handles on the vertices of the line. A link still looks and acts like a line component.