Three-Level ANSI-SPARC Architecture

 Database standard proposed by ANSI SPARK in 1975 is being used worldwide and is the only most popular agreed upon standard for database systems. The Three Level Schema architecture provides us a number of benefits. For accessing data at different levels we have a number of users because not all users have to access data in database at all the database levels. 

The 3 levels architecture allows us to separate the physical representation of data from the users’ views of data. In the database, same data is stored in a specific feasible format and is available to different users in different formats as desired by different users. 

For example, consider we have stored the DOB (Date of Birth) in the database in a particular format, like in the form of dd-mm-yyyy (for example, 28-03-1987). However, the users from different departments may require to view the date of birth in different forms; the examination department may ask it to be displayed as month-day-yyyy (like march-28-1987) the Registrar’s office may ask to display date of birth as mm/dd/yyyy, still the Library may need the in the form of dd/mm/yy. The Three Level Schema allows us to access the data in different formats at the external level, which is stored in a specific format at the internal level

Objectives of Three-Level  Architecture:-

Ø  ANSI-SPARC Three Level Architecture

Ø  All users should be able to access same data  but have a different customized view

Ø  A user’s view is immune to changes made in  other views

Ø  Users   should not need to know   physical  database storage details

Ø  DBA should be able to change database  storage structures without affecting the  users’ views

Ø  Internal structure of database should be  unaffected by changes to physical aspects of  storage

Ø  DBA should be able to change conceptual  structure of database without affecting all  users

External Level:-

v  Users’ view of the database

v  Describes that part of database that is relevant to a  particular user

v  Different views may have different representation of same  data (e.g. different date formats, age derived from DOB  etc.)

Conceptual Level:-

v  Community view of the database

v  Describes what data is stored  in database and relationships among the data

v  Along with any constraints on data

v  The conceptual level represents:

v  all entities, their attributes, and their relationships;

v  the constraints on the data;

v  semantic information about the data

v   security and integrity information.

Internal Level:-

v  The physical representation of the database on the computer. This level describes how the data is stored in the database.

v  storage space allocation for data and indexes;

v  record descriptions for storage (with stored  sizes for data items);

v  record placement;

v  data compression and data encryption  techniques.