You can use the inheritance tool to create inheritances between entities and to join additional children to an inheritance.
Select the Inheritance tool in the Toolbox.
Click and hold inside the child entity and then drag to the
parent entity and release the mouse button.
The link is created between the two entities with a
half-circle symbol in the middle with the arrow pointing to the parent
entity.
[optional] To add further child entities to the inheritance
link, click and hold inside the child entity and then drag to the inheritance
half circle and release the mouse button:
[optional] Double-click the half circle or one of the links to
open the inheritance property sheet, and enter any appropriate properties.