Mapping

The process of transforming request and response between the three levels is called mapping.

There are two types of mapping: Conceptual/Internal Mapping and External/Conceptual Mapping.

1) Conceptual/Internal Mapping

• It connects Conceptual Schema and Internal Schema.
• It defines correspondence between conceptual schema and internal schema.
• If any changes occur at internal schema, conceptual/internal mapping is changed accordingly and conceptual schema remain unchanged.
• There are only one conceptual/internal mapping between internal and conceptual level.

2) External/Conceptual Mapping

• It connects conceptual schema to each external schema.
• It defines correspondence between a particular external view and conceptual/logical schema.
• If any changes occur at conceptual schema, external/conceptual mapping is changed accordingly and external schema remain unchanged.
• There are more than one external/conceptual mapping between external and conceptual level.

Note: We can achieve Data Independence using Mapping.