• The user/external level describes the user or application program view of the database and may be used by several users or programs.



  • The conceptual level describes the organization’s view of the database and lacks implementation detail – it is a logical view of the database.



  • The internal/ physical level describes data storage and access mechanisms and is thus a physical view of the database.



  • The three-level architecture is used to implement data independence.



  • This is achieved via two levels of mapping – between the physical and conceptual schema and between the conceptual and external schema.