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State True or False with reason

Logical data independence is easier to achieve than physical data independence.

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Data Independence in Three Level Schema of DBMS

This is False.

Generally, physical data independence exists in most databases and file environments where physical details are hidden from the user and applications remain unaware of these details. On the other hand, logical data independence is harder to achieve because of a much stricter requirement - it allows structural and constraint changes without affecting application programs.

physical data independence means is to change the view of data, programming level changes are not required.

Example for Physical data independence: Replacing hard disks with SSDs.

Example for Logical data independence: Some changes on table format, should not change the data residing on the disk.

FALSE

The ability to modify schema definition in one level without affecting schema definition in the next higher level is called data independence.

Physical data independence is the ability to modify the physical schema without causing application programs to be rewritten. Modifications at the physical level are occasionally necessary to improve performance. It means we change the physical storage/level without affecting the conceptual or external view of the data. The new changes are absorbed by mapping techniques.

Logical data independence is the ability to modify the logical schema without causing application program to be rewritten. Modifications at the logical level are necessary whenever the logical structure of the database is altered (for example, when money-market accounts are added to banking system). Logical Data independence means if we add some new columns or remove some columns from table then the user view and programs should not change. For example: consider two users A & B. Both are selecting the fields "EmployeeNumber" and "EmployeeName". If user B adds a new column (e.g. salary) to his table, it will not effect the external view for user A, though the internal schema of the database has been changed for both users A & B.

Logical data independence is more difficult to achieve than physical data independence, since application programs are heavily dependent on the logical structure of the data that they access.

Physical data independence means we change the physical storage/level without affecting the conceptual or external view of the data. Mapping techniques absorbs the new changes.

Can anyone explain this point more which is explained by @rajoramanoj

consider two users A & B. Both are selecting the fields "EmployeeNumber" and "EmployeeName". If user B adds a new column (e.g. salary) to his table, it will not effect the external view for user A, though the internal schema of the database has been changed for both users A & B.

If user B adds a new column (e.g. salary) to his table, it will not effect the external view for user A,why it is happening  ?

@Shivani gaikawad This is the basic concept of logical data independence itself. Suppose in a college the faculties and the students use the same database on the same server right? But the views of faculties is different from the view of users. If a faculty adds a column in his view, say 'student attendance', then this won't show in the view of the students.

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Physical data independence is the power to change the physical data without impacting the schema or logical data.

For example, in case we want to change or upgrade the storage system itself − suppose we want to replace hard-disks with SSD − it should not have any impact on the logical data or schemas.
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