Ø Data abstraction – data system are made up of complex data structure the use of data
abstraction interaction with database, the use of data abstraction interaction
with database the developer hide internal detail from the users.The process of
hiding irrelevant detail from user is called data abstraction.
OR
Data abstraction –the
main purpose of database system is to provide users with an abstract view of
the system the system hide certain detail of how data is store, created and
manipulated complexity should be hidden by the database users, which is known
as data abstraction.
There are three levels in data
abstraction –
1. Physical
level
2. Logical
level
3. View
level
1)
Physical level:
This is the lowest level of data abstraction. It describes how data is actually
stored in database. You can get the complex data structure details at this
level.
2)
Logical level:
This is the middle level of 3-level data abstraction architecture. It describes
what data is stored in database.
3)
View level:
Highest level of data abstraction. This level describes the user interaction
with database system.
Example: we are storing customer information in a customer table. At physical level these
records can be described as blocks of storage (bytes, gigabytes, etc.) in memory. These details are often hidden from the programmers.
At the logical level these records can be described as
fields and attributes along with their data types, their relationship among
each other can be logically implemented. The programmers generally work at this
level because they are aware of such things about database systems.
At view
level, user just interact with system with the help of GUI and
enter the details at the screen, they are not aware of how the data is stored
and what data is stored; such details are hidden from them.