Explain the 3 level of Architecture of DBMS?

Answer 1

EXTERNAL LEVEL (highest level)

• The user's view of the database.

• Consists of a number of different external views of the DB.

• Describes part of the DB for particular group of users.

• Provides a powerful and flexible security mechanism by

hiding parts of the DB from certain users. The user is not

aware of the existence of any attributes that are missing

from the view.

• It permits users to access data in a way that is customized to

their needs, so that the same data can be seen by different

users in different ways, at the same time.

CONCEPTUAL LEVEL

• The logical structure of the entire database as seen by DBA.

• What data is stored in the database.

• The relationships among the data.

• Complete view of the data requirements of the organization,

independent of any storage consideration.

• Represents:

- ∀entities, attributes, relations

- constraints on data

- semantic information on data

- security, integrity information

Supports each external view: any data available to a user must

be contained in, or derivable from the conceptual level.

INTERNAL LEVEL

• Physical representation of the DB on the computer.

• How the data is stored in the database.

• Physical implementation of the DB to achieve optimal run-

time performance and storage space utilization.

- Storage space allocation for data and indexes

- Record description for storage

- Record placement

- Data compression, encryption