And also, about the Composition, you say that the component can only exist as a part of the container. Does this mean that a Department class can't be instantiated with a University class? 

Comparing aggregation and composition, I feel obfuscated about the difference between them. Could you give me a concrete example of the difference? Or, is there any related chapter later in the book?

The stars mean how popular the pattern is. 

Unlike the other paper books and online video courses, it's great to see the step-by-step visualization!

I began to learn about design patterns recently. But it seems the strategy pattern matches your requirement.