Inter Schema Mapping:

The mechanism through which the records or data at one level is related to the changed format of the same data at another level is known as mapping. When we associate one form of data at the external level with the same data in another form is know as the external/conceptual mapping of the data. (We have seen examples of external/conceptual mapping in the previous lecture)  In the same way when data at the conceptual level is correlated with the same data at the internal level, this is called the conceptual/Internal mapping.

Now the question arises that how this mapping is performed. Means how is it possible to have data at one level in date format and at a higher level the same data show us the age. This hidden mechanism, conversion system or the formula which converts the date of birth of an employee into age is performed by the mapping function and it is defined in the specific ext/con mapping, for example, when the data at the conceptual level is presented as the age of the employee is done by the external schema of that specific user. Now in this scenario the ext/con mapping is performing the mapping with the internal view and is retrieving the data in desire format of the user.

In the same way the mapping between an internal view and conceptual view is performed.

The figure below gives a clear picture of this mapping process and informs where the mapping between different levels of the database is performed.

Fig: 1: Mapping between External/Conceptual and Conceptual/Internal levels

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