To define a database, you begin by designing a simplified model of the real-world, in which entities represent logical collections of values. For example, you may group the set of details that describe a customer into an entity, and the set of details that describe a material into another entity. The process of designing a database is known as entity modelling.
In a sales order system, entities are required to represent customers, orders and materials. At the design stage, you identify the information that is to be stored. For example, the customer information normally includes the name and address:
Jones Builders, 121 Main Road, Cambridge
A first approximation of the entities in a sales order system is shown here: