Mala Mahadevan begins a series on graph data in SQL Server:
The simplest way to understand a graph data model is that there are just two entities – Nodes, which is what we call Entities in the relational world, and Edges, which are what we call relationships. They are typically represented like below, with the circles standing for nodes, and the arrows for relationships. The emphasis, as we can see is on the bold arrows – because relationships are what graph data is about, with less emphasis on entities/nodes.
Read the whole thing.