THREE LEVELS OF DATA INDEPENDENCE

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THREE LEVELS OF DATA INDEPENDENCE

It divides the entire system into three inter-related but independent modules:

  • Physical Level: Here, information about the location of database objects in the data store is kept. Various DBMS users are unaware of the locations of these objects. The Physical level of database describes how the data is stored in secondary storage devices such as disks and tapes.

  • Conceptual Level: Here, data is represented in the form of various tables. For Example, STUDENT database may contain NAME and COURSE tables, but the users are unaware of their storage. It refers to what kind of data to be stored in a database.

  • External Level: Here, it specifies the view of data in terms of conceptual level tables. It can generate different views of the database for different users. It focuses main on data abstraction. 

Data Independence: It means change of data at one level must not affect the another level.

  • Physical Data Independence: Any change in the physical location of the tables or indices should not affect the conceptual level and external level. This data independence is easy to achieve an mostly preferred by DBMS users.
  • External Data Independence: The data at conceptual level and external level must be independent. This means change in the conceptual level must not affect the external level. For example, adding or deleting the attributes of the table must not affect the view of the table. This type of independence is difficult to achieve in DBMS.

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