Wednesday, 5 October 2011

Conceptual View Level

The middle level in the three-level architecture is a conceptual view level, which is also referred to as logical view  level. It describes the entire structure of database such as entities, attributes, data types, relationships, constraints, and user operations. It hides the details of physical storage structures. The conceptual view level supports the external view level to present the data to end-users as they need. This view is relatively constant and the Database Administrator designs it after determining the present and future information needs of the organization. However, to expand the conceptual view, the Database Administrator adds the new objects to fulfill the requirements of the organization, without affecting the external view.
The conceptual view is defined by means of the conceptual schema, which includes definitions of each of the various conceptual record types. The conceptual schema is a complete description of information of database structure such as every record type with all its fields. It also includes security and integrity rules. The conceptual schema is written in DDL, compiled by the DBMS and stored in its data dictionary. The DBMS uses the conceptual schema to create the logical record interface, which is used by the external record of a particular user to present data to that user. Actually, conceptual view level is a collection of the logical records.