DBA should be able to change the conceptual structure of the database without affecting the user's.All users should be able to access the same data according to their requirements.The users of the database should not worry about the physical implementation and internal workings of the database such as data compression and encryption techniques, hashing, optimization of the internal structures etc.The approach in which a particular user needs to see the data may change over time.
Different users need different views of the same data.This separation is desirable for the following reasons: Thus it separates the user's view from the physical structure of the database. The main objective of three level architecture is to enable multiple users to access the same data with a personalized view while storing the underlying data only once. In Conceptual / Internal mapping, DBMS transform the request from the conceptual to internal level.In External / Conceptual mapping, it is necessary to transform the request from external level to conceptual schema.Mapping is not good for small DBMS because it takes more time.Mapping is used to transform the request and response between various database levels of architecture.The three-schema architecture is as follows: It breaks the database down into three different categories. The three schema architecture contains three-levels.The three schema architecture is also used to separate the user applications and physical database.This framework is used to describe the structure of a specific database system.The three schema architecture is also called ANSI/SPARC architecture or three-level architecture.
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