Ability to modify the one level without affecting other level of scheme is called data independence
It is of 2 types
1- Physical data independence
Ability to modify the physical level schema without causing application program to be rewritten.
It improve performance
2• logical data independence
Ability to modify the conceptual level schema without causing application program to be rewritten.
it is harder to achieve as application programs are heavily dependent on it.
DATA DEFINITION LANGUAGE -defines the database schema ,the definition of database. Also known as DDL
DATA MANIPULATION LANGUAGE
also known as dml use to retrieve,delete,modify,insert
Types of DML
1- Procedural • what data is needed and how to get it
2 Non Procedural• what data is needed. Procedural generate more efficient codes.