Networks are all around us. We use the word network to refer to many different types of connected things: multiple computers hooked together, a system of cities connected by small roads and large highways, a group of people who all work in the same industry, a series of television stations that broadcast common programming. In common usage, the word network can refer to almost any set of interconnected entities.
From a data mining perspective, however, our use of the word network is more precise. We use the word network to refer to a system that can be represented by a graph made up of nodes and links. In our specialized vocabulary, nodes are the things being connected, and the links are the relationships between the nodes. The collection of all the nodes and links is called a graph. Note that we are using the word graph in its mathematical sense, not in the sense of a visualization, like a bar graph or a line graph. In graph theory vocabulary, nodes are also called vertices...
