Why do we need mappings between schema levels and how do different schema defition languages support this architecture?
Answers
Mapping is mainly needed between schema levels for two reasons. ... The mapping also helps in different kinds of transformation. A DBMS (database management system) has three schema levels as given below: Physical or internal schema
There are three levels of schema in DBMS:
Physical schema Internal schema : Provide the concept that defines the how data is stored in the computer.
Conceptual schema or logical schema: Describe the structure and constraints for the whole database for a community of a user or implementation of a data model.
External schema or view level: Describe the various user view (Different view and different representation of the data).
The Process of transforming request and results between three level it's called mapping.
There are the two types of mappings:
Conceptual/Internal Mapping
External/Conceptual Mapping