The Three-Level ANSI-SPARC Architecture

The American National Standards Institute (ANSI) Standards Planning and Requirements Committee (SPARC)=>Recognized the need for a three-level approach with a system catalog
Provides a basis for understanding some of the functionality of a DBMS.

Objectives of Three-Level Architecture
The objective of the three-level architecture is to separate the users’ view(s) of the database from the way that it is physically represented. This is desirable since:

-It allows independent customised user views: Each user should be able to access the same data, but have a different customised view of the data. These should be independent: changes to one view should not affect others.

-It hides the physical storage details from users: Users should not have to deal with physical database storage details. They should be allowed to work with the data itself, without concern for how it is physically stored.

-The DBA should be able to change the database storage structures without affecting the users’ views: From time to time rationalisations or other changes to the structure of an organisation’s data will be required.

-The internal structure of the database should be unaffected by changes to the physical aspects of the storage: For example, a changeover to a new disk.

-The DBA should be able to change the conceptual or global structure of the database without affecting the users: This should be possible while still maintaining the desired individual users’ views.