First pattern which I'll try to explore is a structural pattern - Facade.
Before we go to the pattern I think we must understand a concept of subsystem.
Subsystem is a part of large system that consists of a set of elements and relations.
Let's look for simple example for better understanding.
Here you can see a system which consists of four subsystems : UserInterface, OrderManagement, SeatingManagement and Database. Each subsystem has own logic as well as relations to another subsystem(s).
