Data abstraction

Data abstraction in dbms means hiding data at different levels to aachieve data independence.Data abstraction levels are placed between users and database to achieve consistency,independence and controlled access.There are three level s of data abstraction as shown in diagram.

Physical level

Physucal level in data abstraction is the lowest levell of abstraction which describes how data data is stored in raw form in data structure,how data is organzied at low level.Physical level of abstracts (hides) low level hardqare implmentation of database.Physical level absreacts these ;ow level data from users to make users to use database easily and with convivence.

Logical level

Llogical level of data abstraction is thenext level above physical level which describes what data is stored and what are the relationships between them,what constraints exists bwrween data.At logical level small small simple data structure is used to store data.Logical level abstracts data sotred by the users from physical level and hardware implmentation of a dbms.

View level

View level of data abstraction provides a protion of an database to the users whcih they want to access at a time, for which they are allowed or aurhoeized for.There any numbers of biews for different users autheoized for operation like read,create,update etc.

View level abstracts the entire database from the user and allow users to access e particular portion of the database.

Data independence

Data Independence is the separation of data and application programs means that user can access its data from any where at any time independently.There are tqo types of data independence.

Conceptual data independence

Concepptual data independence means that changws made at loical level does not affect view level.Any changes in logical structure of database does not effect application programs of view level of the database system.

Physical data independence

Physical data independence mwans that changes made at physical level does not affect logical lwvel .Any changes in physical structure of database does not effects on the logical level of the database system.