Relational Terminology: Entities

An entity is anything about which the system needs to store information.

When you begin to design your data model, compiling an initial list of entities isn't difficult. When you (or your clients) talk about the problem space, most of the nouns and verbs used will be candidate entities. "Customers buy products. Employees sell products. Suppliers sell us products." The nouns "Customers," "Products," "Employees," and "Suppliers" are all clearly entities.

Most entities model objects or events in the physical world: customers, products, or sales calls. These are concrete entities. Entities can also model abstract concepts. The most common example of an abstract entity is one that models the relationship between other entities—for example, the fact that a certain sales representative is responsible for a certain client or that a certain student is enrolled in a certain class.