Monday, 1 May 2017

Physical data independence in database management systems

Physical data independence in database management systems, Define physical data independence, Explain physical data independence with example, examples of physical data independence in dbms


Physical Data Independence


The ability to change the physical schema (internal level – this level is about “how the database is stored?”) without affecting the next higher level conceptual schema (logical or conceptual level – this level is about “how the database is designed?”) is called physical data independence.

Example:

  • Physical level deals with storage and access methods of database.
  • Conceptual level deals with the overall structure of a database.

Let us assume a table STUDENT with the following schema;
STUDENT (Reg_No, SName, DOB, Phone)
This is conceptual schema.
Let us suppose that we would like to change the size of SName attribute of STUDENT table. For doing this, do we need to modify the schema of STUDENT? No. Without changing the schema, we would increase or decraes the size of an attribute. This is called physical data independence.

In simpler terms, schema of database is conceptual level and how the schema is created and stored in a database is physical level.

Conceptual level
Physical level
STUDENT (Reg_No, SName, DOB, Phone)




It defines the structure of STUDENT table
CREATE TABLE Student
( Reg_No CHAR(10) Primary key,
SName VARCHAR(30),
DOB DATE,
Phone NUMBER(10) UNIQUE);

This defines the data type, size, and constraints of a table’s attributes.

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