Database Data Structure

Data Independence

The ability of modifying a schema definition in one level without affecting a schema definition in a Higher Level is called Data Independence.

Types:

Logical Data Independence

• The ability to modify the conceptual scheme without causing application programs to be re-written.

• Immunity of external schemas to change in conceptual schema

• Usually done when logical structure of database is altered

Physical Data Independence

• The ability to modify the internal schema without having to change the conceptual or external schemas.

• Modifications at this level are usually to improve performance.

Schema of a database system is its structure described in a formal language supported by the database management system (DBMS) 

• Refers to the organization of data to create a blueprint of how a database will be constructed (divided into database tables).
• The formal definition of database schema is a set of formulas (sentences) called integrity constraints imposed on a database.