Three Level Architecture

Three Level Architecture: An early proposal states for a standardized terminology and architecture for database system were developed and published in 1971 by DBTG (Data Base Task Group) appointed by CODASYL. A similar architecture and terminology were developed and published in 1975 by SPARC (Standards Planning and Requirement Committee) of American National Institute (ANSI) for the data representation. As a result of these and later reports, database can be viewed at three levels, known as external, conceptual and internal levels. These levels form three level architecture . These levels are represented by three schemas or three models known as three level schema or Three Schema Architecture for representation of the data.

The purpose of the three schema architecture is to separate the user applications and the physical database of the same file. The reason of this separation are:

  1. Different users need different views of the same data with in the same file.
  2. User should not have to deal directly with the physical database storage details.
  • The DBA should be able to change the database storage structure or storage device without affecting other user’s views and applications of same file data.

These level are

  • External Level
  • Conceptual Level
  • Internal Level