Mapping is a process of converting on level to another level. There are two levels of mapping:
• From the conceptual level to the internal level
• From the external level to the conceptual level
Conceptual / Internal Mapping:
The conceptual/internal mapping defines the association between the abstract view and stored database. It specifies how conceptual records and fields are represented at the internal level. If stored data is changed with structural point of view, then the conceptual mapping must be changed accordingly so that the conceptual plan can remain steady.
External / Conceptual Mapping:
An external/conceptual mapping defines the correspondence between a particular external view and the conceptual view. In general, the differences that can exist between these two levels are similar to those that can exist between the conceptual view and the stored database. For example, fields can have different data types, fields and record names can be changed, several conceptual fields can be combined into .a single field. Any number of external views can exist at the same time. Any number of users can share a given external view and different external views can overlap each other.
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