3-Level of Abstraction :-

➺ Abstraction refers to essential features without showing background details of database systems.
➺ Database systems are composed of complex data structures.
➺ The developer uses the level of abstraction to reduce the complexity of the user and easy retrieval of data from the database.

◆ There are mainly 3 level of data abstraction :-

➺ It is a low-level representation of the whole database.
➺ It shows how data are actually stored is called physical schema.
➺ Database Administers (DBA) work on a physical schema that manages by DBMS.
➺ Physical schema manages the hard disk in the database.
➺ It is the lowest level of data abstraction.
➺ It tells us what data is stored.

➺It is next higher level or intermediate level.
➺ It represents structure of entrie database for user.
➺ In this we design structure of database, create table and show relationship between table.
➺ It is an abstract representation of the database content.
It hides information about the physical storage.
➺ Defines all Database entities, Attribute And Relationships.
➺ Create table, Database design, ER- Model etc.
➺ Ex:- Student ( Rollno, name, Address).

➺ It is the top or highest level of data abstraction that is used by the user to view data.
➺ Only some portion of the data is viewed by the user.
➺ External schema is connected with the user In which provides a different view to the different end users.
➺ External schema is hidden from the conceptual schema and physical schema.
➺ In External schema didn't show the user in which table data is stored and the relationship between tables. It only shows data to view them.
➺ Each user views the data in terms of an external view defined by an external schema.
➺ External level or view level is nearest to the user.

You might like this :-

○ History of computer
○Normalization in DBMS
○Codd's 12 Rules
○DBMS vs RDBMS