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Data Independence

The three-schema architecture is used to explain the concept of data independence which tells us to change the schema at one level without affecting the schema of another higher level. We have two kinds of data independence-

a) Logical Data Independence: It defines the capacity to change the conceptual schema without changing the external schemas. The users should be unaware of the changes are made at the conceptual level. While expanding, reducing, changing constraints at the conceptual schema, users should be unaware of that.

b) Physical Data Independence: It defines the capacity to change the physical schema without affecting the conceptual schema hence the external schema. Changes to the internal schema may be needed if some physical files were reorganized in order to improve the performance of retrieval or update.