Get to know what an ER Diagram is through use cases and examples. Explore the notations for the essential components of an ERD. Entity-relationship diagrams (ERDs) are used to visualize data and relationships among the entities of a system. At its core, an ER Diagram explains the logical structure and the flow of information within a data model. To do so, an entity-relationship diagram highlights entities, attributes, and relationships through predefined symbols for effective visualization of the architecture.