Database 3 Level Architecture Basic Definitions and the Overviews of the DBMS Architecture for students, Database 3 Level Architecture concept.
Database 3 Level Architecture
Internal level: It is the lowest level of data abstraction that deals with the physical representation of the database on the computer and thus is also known as physical level.
Conceptual level: This level of abstraction deals with the logical structure of the entire database and thus, is also known as logical level.
It describes what data is stored in the database, the relationships among the data and complete view of the user’s requirements without any concern for the physical implementation.
External level: It is the highest level of abstraction that deals with the user’s view of the database and thus, is also known as view level.
In general, most of the users and application programs do not require the entire data stored in the database the requests and results between various levels of DBMS architecture is known as mapping.
Also Read: DBMS – Architecture
Data independence is the ability to change the schema at one level of the database system without having to change the schema at the other levels.
Data independence is of two types, namely, logical data independence and physical data independence.
Logical data independence: It is the ability to change the conceptual schema without affecting the external schema or application programs.
The conceptual schema may be changed due to change in constraints or addition of new data item or removal of existing data item, etc from the database.
Physical data independence: It is the ability to change the internal schema without affecting the conceptual or external schema.
An internal schema may be changed due to several reasons such as for creating additional access structure, changing the storage structure, etc.