Building a graph is not enough; we also need the ability to search through it. To make it easier to build search algorithms, it is useful if we can represent the graph and its connections in a different way; adjacency matrix being one such representation. An adjacency matrix is a means of representing which vertices (or nodes) of a graph are adjacent to which other vertices.

He includes some sample code to extract the data from a graph (built with the PEAR Structures_Graph package) and create a basic "table" of information about each nodes' connections.