Entity Relationship Model(E-R Model):
The Entity Relationship(E-R) data model is based on concept of real world that consists of a collection of basic objects called 'entities' and relationship among the object.
An Entity in an E-R Data Model is a real world object having properties called Attributes.
Every attribute is defined by set of values called domain.
Example: In a school database, student is considered as an entity.
Student has various attributes like SName, SAge, SClass etc.
Relationship:A logical Association among several entities.
Example: In the above example we add 'Teacher' entity with attribute T_Name, T_class. So student and teacher can be relationship with relation class.
One entity can have 2,3 more relationship with other entity.