In systems analysis and design “entity” has two different meanings: An external entity refers to a person, office or thing that interacts with the system. Internal entities, or just entities are persons, places, or events that will be stored in the database. Entities are referred to by the generic name rather than a specific person or place: “Payroll” rather than “Room 283”, or “Student” rather than “David Adams” for example. Entities are usually singular: “Employee” rather than “Employees.”
In diagrams, entities are shown as squares.
In a college registration system, there are entities such as Student, Professor, Course, Section, and Room. In a store the common entities are Customer, Product, Supplier, and Salesperson.
Entities and Attributes