What are Networks?


1 What is a Network?

These days, networks and talk about “social networks” is everywhere. It was not always so, the discipline of social network analysis (SNA) developed quietly during the 1960s and 1970s out of scattered lines of work in anthropology, sociology, psychology, mathematics, and communication. It wasn’t until the 1970s that a formal group was founded to study social networks (the International Network of Social Network Analysis [INSNA]). Today, network science is an interdisciplinary field uniting physics, computer science, biology, brain science, sociology, anthropology, economics, and a variety of other fields. All are come together around the idea of a “network.”

Point and line plot of a network. Figure 1.1: Point and line plot of a network.

So what is a network? Minimally, a network is composed of a set of units or entities. These are some times called nodes or vertices, however what makes these units into a network is the fact that at least some pairs of them are joined by a set of links or ties. These are also sometimes called edges. So a network is essentially a set of nodes some of which are linked together. In social networks, the nodes can be people and the connections can be any type of social tie (e.g., friendship, enmity, co-working), whether positive or negative, between them. In future lessons, we will discuss the different types of ties that can exist in social networks as well as the major social network theories that have been developed by sociologists, anthropologists, and organization theorists to explain why these types of ties exist, how they work, and what benefits (or drawbacks) they have for people and organizations.

Types of Networked Systems.

Figure 1.2: Types of Networked Systems.

In a point and line plot such as the one shown in figure 1.1 networks are some times shown as pictures. This kinds of pictures are also sometimes called sociograms or network diagrams. The convention in these kind of depictions of networks is that the nodes (e.g., people) are drawn as circles (or some other polygon such as a triangles or squares) and the connections, ties, or links between people are drawn as lines or sometimes, if some kind of direction is implied, as arrows. This way of representing networks is some times called a “graph,” although we will see that the idea of a graph is a little more abstract than just a picture. So in this class we will make a strong differention between pictorial network representations, and the mathematical concept of graph. When referring to the former, we will use the term plot or network diagram, reserving the term graph for the mathematical object. In future lessons, we will get into more details about pictorial (and non-pictorial) ways of thinking about networks and how they connect to other ways of representing them.

2 Types of Networks

Network of Characters in Game of Thrones. Figure 2.1: Network of Characters in Game of Thrones.