Explanation: The subschema differs from the schema in that one denotes the appearance of data in the Database Base Management System (DBMS) while the subschema which is also referred to as the external schema is that subset of the schema is visible or relevant to the user. Thus, It is the view of the database which is visible to an application program. Virtual tables in a database usually represents an object structures like a table which is the result of running certain database commands or functions such as the create table, view, select and so on. Virtual tables are not stored directly in database files.
