The three-schema architecture divides the database into three-level used to create a separation between the physical database and the user application. In simple terms, this architecture hides the details of physical storage from the user.
The database administrator (DBA) responsible is to change the structure of database storage without affecting the user’s view. It deals with the data, the relationship between them and the different access methods implemented on the database. The logical design of a database is called a schema.
This architecture contains three layers of database management system (DBMS) −
The three layers of the DBMS are pictorially represented below −
View 1 − Library User
Roll number, Name, Address, Book Number, Date of Issue, Date of Return
View 2 − Account office
Roll Number, Name, Fees
Conceptual View for view 1 and view 2 are −
|Field Name||Data type(size)|
|Date of Issue||varchar(20)|
|Date of return||varchar(20)|
Internal View on hard Disk
|Roll Number||Type=byte(20), offset(starting address) =20|