Entity - Relationship Model

                                                   

ENTITY-RELATIONSHIP MODEL

The entity-relationship (E-R) data model uses a collection of basic objects, called entities, and relationships among these objects. 

An entity is a thing or object that is different from other objects. Entities are described in a database by a set of attributes. The extra attribute ID is used to identify an instructor uniquely. A unique instructor identifier must be assigned to each instructor.

A relationship is an association among several entities. The set of all entities of the same type and set if all relationships of the same type are termed as entity set and relationship set, respectively.

The overall logical structure of a database can be expressed graphically by an entity-relationship(E-R) diagram. 

A Sample E-R Diagram

• Entity sets are represented by a rectangular box with the entity set name in the header attributes along with.
• Relationship sets are represented by a diamond connecting a pair of related entity sets. The name of the relationship is within the diamond box.