The three schema architecture of DBMS is also known as ANSI/SPARC architecture or three-level architecture. This architecture describes the physical structure of the database. It also defines how the data is visible to the user in the specific database system. This architecture hides the details of the physical database from the user who uses the database system.
It provides the three different views of the database system. It is a design that breaks the database into three different parts according to the use and the structure.
Following are the different levels of data abstraction in the three schema architecture of DBMS:
- External Level
- Conceptual Level
- Internal Level
External Level
This type of level is also known as View level. It is the highest level in the three schema architecture and very closer to the end-user. It is that level of three schema architecture, where the user interacts to access the data from the database using the conceptual or logical level.
The external level provides the different views of the same database to each user. At this level, users access only some parts of the database rather than the entire database. This schema or level hides those database details which are not related to the users.
Conceptual Level
This type of level is also known as the Logical level. It is the middle level in the three schema architecture. This level comes between the user and the physical storage. For each database, there will be only one conceptual schema.
It is that level of three schema architecture, which describes the whole design or structure of the database to the users. It describes what type of data is to be stored in the database, and also describes the relationship among those stored data. It hides all the information about the structure of physical storage. It maintains data consistency and provides data integrity as well as security to the data.
Internal Level
This type of level is also known as the physical level. It is the lowest level in the three schema architecture. It is very closer to physical storage. It is that level of three schema architecture, which describes how the data is actually stored in the database systems or the storage devices. This level defines the structure of the physical storage. This level is only operated by the Database Administrators (DBA).
Objectives of Three Schema Architecture
Following are the various objectives or goals of the DBMS three schema architecture:
- The main aim or objective of this architecture is that it provides the data abstraction.
- Different users can easily access the same data from the same database by different views.
- DBA can easily change the conceptual structure of the database without affecting the view of end-users who are currently using the same database.
- The user need not to interact with the details of physical storage.