ENTITY AND ATTRIBUTES

Entity : An entity is a "thing" in real world, with an independent existence. It may have a physical existence in the real world or it may be an object with a conceptual existence.

Each entity has a set of particular properties that completely describe it, in the context of the mini-world model.

Attributes : The entity properties are called attributes. Attributes are properties used to describe an entity; for example an Employee entity may have a Name, Employee number, Address, Sex, Birth Date etc.

Several types of attributes occur in the ER model. They are;

1. Simple : Each entity has a single atomic value for the attribute.

2. Composite : An attribute may be composed of several components.

3. Multi-valued : An entity may assume multiple values.