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
Levels of Data Abstraction
1. 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));
2. 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
3. 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
1. Conceptual Level
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
1. Logical Data Independence
DBMS architecture provides two types of data independence
ex: Adding a new entity in the conceptual level should not affect the external level
2. 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
