It consists of nodes and lines, representing many objects and their relationships. Mathematically, the network is a graph, which is generally considered as a weighted graph. In addition to the mathematical definition, the network also has a specific physical meaning, that is, the network is an abstract model from a certain kind of practical problems. In the computer field, the network is a virtual platform for information transmission, reception and sharing. Through it, the information of various points, surfaces and bodies is linked together, so as to realize the sharing of these resources. Network is the most important invention in the history of human development, which has promoted the development of science and technology and human society.

Before 1999, people generally thought that the network structure was random. However, people didn't realize the complexity of the network until Barabasi and Watts discovered the scale-free and small-world characteristics of the network in 1999 and published their findings in the world-famous magazines Science and Nature respectively.