As the database designer, you must understand all data used in your corporation. Once you have determined the user's information requirements, you need to develop a comprehensive picture of the corporation's data. Your logical design must include a complete description of this data.
Entity-relationship diagram
To represent the total picture, you can use the entity-relationship approach to logical design. With this approach, you develop an entity-relationship diagram, which serves as a model of the entire corporate enterprise. This diagram visually represents all data relationships that exist within the corporation.
Entities
If data tables allow you to see the "trees" in a database, the arrangement of entities in an entity-relationship diagram helps you to represent the "forest." An entity is any general category of information used for business data processing. For example, the DEPARTMENT entity might describe information about the departments in a corporation, while the EMPLOYEE entity might describe company employees.
Entity-relationship diagramming
When two or more entities in a database share a relationship, their relationship can be graphically depicted on the entity-relationship diagram.
In the diagram below, the DEPARTMENT and EMPLOYEE data entities are related through the relationship BELONGS TO.
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