Data Abstraction and Data Independence in DBMS

Conceptual level

• • It describes the logical structure of the database
  • Specifies what type of data can be stored in the database by defining the data type and data type signs and constraints like (primary key foreign key )etc
  • It also specifies the relationship between tables

Example : Create table emp(id num(5) primary key ,name varchar(10));

External level

• • External level describe users view of the database
  • It provides security mechanism i.e some users can access only a certain portion of data, it depends upon the database administrator which users can access the conceptual level and at what extent

Internal level

• • This is the lowest level of abstraction describes how physical data is stored
  • It provides details about the complex data structures that are used for storage of data
  • Internal level provides indexes and  clusters  to control and manage the physically  stored data in hard disk