DBMS #05: Data Independence

The three levels of schema provided by the DBMS are:

1) Internal/ physical schema, which describes how the data is actually stored.

2) Conceptual/ logical schema, which describes what data is present in the database (and its meaning), and

3) External schema, which describes the use of the data. This is derived from the conceptual schema and not physically stored in the database.

Physical data independence is a measure of how much a physical schema can be changed without affecting the logical schema. Similarly, we can define logical data independence. Logical data independence is harder to achieve, and hence changes are more possible to the external schema when there are changes in conceptual schema.

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