Three Schema Architecture Three Schema 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…
The external level or view is closest to the users in the data file. It is concerned with the way the data is viewed by individual users of retrieving the information. You can say that external level is the individual user level in the three schema architecture for representing the data and information. A user can either be an application programmer or an end-user but DBA is an important special case that manages and control the database.
The external level consists of many different external views or external models of the database of the same organization. Each external view describes the part of the database that a particular user group is interested in and hide the rest of the database from that user group for data consistency and data integrity. In addition, different views may have different representation of the same data.
The external views are defined by means of external schemas that are written in the Data Definition Language (DDL). Usually, the DBA writes an external schema to create a user view of the data file of the organization. Each user’s schema gives a complete description of each type of external record that appears in the user’s view. The external schema are compiled by the DBMS and stored in its Data Dictionary.The DBMS uses the external schema created for specific user, to create a user interface to access data of the database. Thus the user-interface created through external schema accept and display information in the format the user expects. It is also act as barrier to hide information of database from users that is not permitted to him. Typically, it hides the conceptual, internal and physical details from users.