Data Model :- A collection of conceptual tools for describing data, data relationships data semantics and constraints.
ER-Model :- This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.
Object Oriented model :- This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.
Entity:- It is a 'thing' in the real world with an independent existence.
Entity type:- It is a collection (set) of entities that have same attributes.
Entity set:- It is a collection of all entities of particular entity type in the database.
