DBMS: What is extension and intension?

Question

What is Data Model?
What is E-R model?
What is Object Oriented model?
What is an Entity?
What is an Entity type?
What is an Entity set?

Answer 1

Extension: It is the number of tuples present in a table at any instance. This is time dependent.
Intension: It is a constant value that gives the name, structure of table and the constraints laid on it.

Answer 2

The description of data base is called in tension or database schema,which is specified during database design and is not expected to change frequently.
The actual data in a database may change quite frequently.The data in a database at a particular moment in time is called a extension or database state or snapshot.