Three level of database Architecture OR Levels of data abstraction ( DBMS )

Three level of database Architecture OR Levels of

data abstraction:

There are three levels of data abstraction (Database).

1. Physical level (Internal Level):

It describes how a record (e.g., customer) is stored in the database.

Features:

· Lowest level of database.

· It describes how data are actually stored.

· It describes low-level complex data structures in detail.

· Provide optimal run time performance and storage space size.

2. Logical level (Conceptual Level):

It describes what data stored in database, and the relationships among the data.

Features:

· It is next-higher level of database. Here whole Database is divided into small

simple structures.

· Here the aim is ease of use. (mean freedom from problems)

· It represents entities, attributes, relations, security, data integrity etc.

· Generally, database administrators ( DBA ) work at logical level of abstraction.

3. View level (External level):

It hides details of data types. Views can also hide information (e.g., salary) for security

purposes.

Features:

· It is the highest level of database.

· Provide a powerful security mechanism by hiding a part of the database from

group of users only.

· This view hides all complexity.

· It exists only to simplify user interaction with system.

· The system may provide many views for the whole system.

Customer_Details: Cust_id: 101 Loan_no: 1011 Amount: 9000	External Level
CREATE TABLE Cust_Details( Cust_id number(5), Loan_no number(5), Amount number(10));	Conceptual Level
Cust_id TYPE=BYTE(4); OFFSET=0 Loan_no TYPE=BYTE(4); OFFSET=4 Amount TYPE=BYTE(7); OFFSET=8	Internal Level