The Hierarchy window shows a mini picture of the composition of the current element with respect to other elements.
This information is derived from relationships with child or related classes. Relationships shown in the hierarchy include aggregation, inheritance and dependency; embedded elements are also shown. This helps extend the picture of where an element exists in the model space.
Display of each type of relationship is optional, and can be toggled using the toolbar for the hierarchy window.
Tip: You can alter the maximum number and the initial number of levels that the hierarchy opens to by selecting the Tools | Options menu option and, on the General tab, updating the Max Hierarchy View Depth and Open Hierarchy View to fields.