Introduction

In the real world, there are many entities that are composed of a group of objects and connected with each other by certain laws, which is called a system. There are large systems in nature, such as the solar system and the Milky Way. Such systems exist naturally without the influence of human beings and are called natural systems. For example, the systems composed of organisms and atoms are all natural systems. The system formed by human design is called an artificial system, such as a production system, transportation system and communication system. There are also systems that combine artificial systems with natural systems, called integrated systems, such as navigation systems.