There are 3 views of approach in database management systems – External, Conceptual and Internal. These approaches have been used to develop information systems for the last 4 decades. The approach requires that you use 3 separate views in system development. The conceptual model plays the central role in achieving data integration.
External Data Level – In this approach, the schema can present data as a set of relations. It will specify a view of the data based on the conceptual level. This scheme is customized according to the needs of a specific group of users. Some part of the stored data is not allowed to be viewed by certain users and it can have certain security levels.
Examples of security levels in external data level include not allowing students to view the salaries of the faculty; preventing the faculty from seeing the payment or billing data. In this system, the information taken from stored data may be seen as if it was stored.
In external data level, the applications are developed on the basis of an external schema, and the view gets computed whenever it is accessed. However, it doesn’t get stored. It is possible to deliver separate external levels to different groups of users. The conversion from the external to conceptual level takes place automatically during run time. It is possible to change the conceptual schema without the need to change application.
Conceptual Data Level – It is also referred to as logical level. This level will hide the particulars of the physical level. The conceptual model will present data in the form of a set of tables in a relational model. There is automatic access within the conceptual and internal levels by the management system. It is possible to change the internal level schema without the need to change application. The management system will alter mapping from conceptual to internal.