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Data Abstraction and Data Independence in DBMS

April 7, 2021

Data Abstraction and Data Independence

Data abstraction and data Independence talks about levels of data storage and Organisation, security, uses view of the database, etc

Data Abstraction:

Definition: Data abstraction refers to the hiding of details from users at certain levels, for authentication and security purpose

Any DBMS architecture mainly consists of three levels of

    1. Conceptual level
    2. Internal  level
    3. External level
Data Abstraction and Data Independence

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

Data Independence

These levels of abstraction provide data independence i.e is all the transactions or  changes made at one level are unaffected to other levels

DBMS architecture provides two types of data independence

    1. Logical data independence
    2. Physical data independence

Logical data independence

Logical data Independence states that external level is completely unaffected are free from any changes that are made at the conceptual level and vice-versa
ex: Adding a new entity in the conceptual level should not affect the external level

 

Physical data independence

Physical data Independence states that conceptual level is completely unaffected are free from any changes that are made at the internal level and vice-versa
ex: Adding a new entity in the internal level should not affect the conceptual level