Notes > Database Systems > Mappings and Data Independence
Mappings between the different database schemas allows for data independence. The Database Management System (DBMS) is responsible for managing these mappings and checking the schemas for consistency.
Internal-Conceptual mappings enable the DBMS to find records within the database storage medium that correspond to the logical record in the conceptual schema. External-Conceptual mappings enable the DBMS to match names of data items etc... in the user's view with the parts of the conceptual schema that correspond to those items.
Data Independence means that the higher levels of the database model are designed to be unaffected by changes to the lower levels (internal and physical). There are two types of Data Independence.
- Logical data independence
- Physical data independence
Logical Data Independence involves the external schema being unaffected by changes in the conceptual schema. For example, a new field can be added to a table (relation) without any changes to application programs etc... being required.
Physical Data Independence means that the conceptual schema is not affected by changes made to the internal schema. An example of a change to the internal schema would be changing the storage device used to store the database data. This would not affect the conceptual or external schemas / layers.
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