This SQL ER Diagram Example aids in the explanation of database logical structure. Entities, attributes, and relationships serve as the foundation for ER diagrams. Rectangles are used to represent entities, ovals are used to define attributes, and diamond shapes are used to describe relationships in ER Diagrams. At first glance, an ER diagram appears to be a flowchart. However, the ER Diagram includes many specialized symbols, and their meanings distinguish this model. The ER Diagram's purpose is to represent the entity framework infrastructure.