This ER Diagram for Hospital Billing System illustrates how data objects in a database relate. A database designer can use an ER diagram to sketch the system's structure using only three basic elements: entities, attributes, and relationships. An ER diagram is the first step in designing a database, and an ERD assists the designer in avoiding problems later on when building the database. An entity-relationship chart can also be used to document and analyze an existing system in the opposite direction. ER diagrams are also simple enough for non-technical colleagues to understand that they can be shared for feedback and requirement definition.