We regard network just as a graph. There are nodes, which are connected to form edges. In a social network, each individual is a node, people are connected to each other in accordance with friend relationship.
Each node has ? edges. The more edges, the greater connectivity. Just like the more friends you have, the greater influence you have. For example, we issued a free trial sample to consumer. If the consumer feels satisfied, he will buy it, and recommend to his friends. As the manufacturer, we certainly hope that the samples are distributed to more influential people, because they will be passed on to more nodes, which will bring more potential customers. We know that graph includes directed graph and undirected graph. The difference between them is whether the links between nodes are bidirectional. Facebook and Renren are undirected graphs: If you are my friend, I am your friend. However, Twitter and Sina Weibo are directed graphs: I follow some people, and there are also people follow me. This is a relationship from one node to another node, not reversible.
For example, Zhao Te is followed by many people on blog, then there are many nodes pointing to him, who is on a high in-degree centrality. However, in-degree high node is not always the most valuable. Another example, an article has a high in-degree. A lot of people have quoted this paper.This article may cover a valuable question to research, but it may make obvious mistakes so that everyone having read the research paper will say: "Go for a look of this article, the author is so funny!"
