https://www.visual-paradigm.com/guide/uml-unified-modeling-language/uml-aggregation-vs-composition/
https://www.geeksforgeeks.org/system-design/generalization-in-ooad/
https://medium.com/@prabathmail/generalization-in-the-context-of-software-development-bcb6191f06f9
https://people.cs.vt.edu/~kafura/ComputationalThinking/Class-Notes/generalization.html