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Data Abstraction and Data Independence in DBMS
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
- Conceptual level
- Internal level
- External level

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
- Logical data independence
- 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
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