This page is inspired by rule four in Geert Bellkeens' blog post 5 rules for better UML diagrams.
The elements that are highest in a hierarchy should also be placed highest in a diagram. In other words:
- Subclasses should be placed bellow their parents.
- In aggregation relationships, the element on "whole-side" should never be bellow the element on the "part-side".
- For realizations, the original element should be on top.
In the first diagram bellow, subclasses are placed above their mothers. This makes it difficult to understand the hierarchy in the diagram:
Instead, the subclasses should be aligned bellow their mother, like in the figure bellow:
The figure bellow illustrates an aggregation, with the "whole-side" on top. This is also a hierarchy since DQ_EvaluationMethod is a part of DQ_Element.