The people responsible for developing the database schema and those who write application programs for use by non-technical users
have knowledge of the entire schema, including direct access to the base tables of the database.
However, it is usually undesirable to have end users working directly with base tables, primarily for security reasons.
The relational data model includes a way to provide IT users with their own view of the database.
This view hides the details of the overall database design and prohibits direct access to the base tables which should not be accessed.