Schema and Subschema in DBMS
Schema in DBMS:
The term schema shows an overall structure (organization) of all data-items including their record types stored in a database. To set up a database, we must first define its structure and the schema definitions. This is done by identifying the characteristics of each field contained in a database.
A good way to begin defining the schema of a database should also consider the possible future needs of all types of users. That is all possible fields that may be needed shortly should be included in the database structure at the time of defining it.
Although it is possible to modify the database structure at any time, making such a modification is time-consuming. Hence, it is always better to design a database very carefully at the beginning itself and minimize the need to modify it later.
Subschema in DBMS:
The term Subschema refers to an application programmer’s view of the data-items and record types which the user would use. Many subschema can be derived from one schema. The subschema is also referred to as the logical view.