Why do we need mappings between schema levels?
Answers
Mapping is primarily needed between schema levels for two reasons. These are schema matching and visualization. The mapping also helps in different kinds of transformation. A database management system has three schema levels as given below:
Physical or internal schema – Helps to define how data is stored in the computer
Conceptual or logical schema – Describes the structure for the entire database with the constraints to be implemented for the database.
External or view level schema – Define the various views and data representations.
The two mappings are internal mapping and external mapping.
The need for mappings between schema levels appears due to visualization and schema matching. This mapping helps in different types of transformation. A Database Management System has three schema levels; Physical or internal schema, Conceptual or logical schema and External or view level schema. However, the mapping they follow is internal and external mapping.