What Is The Difference Between Control & Uncontrolled Redundancy?


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Redundancy is when the same fact is stored multiple times in several places in a
database. For example, in Figure 1.5(a) the fact that the name of the student with
StudentNumber=8 is Brown is stored multiple times. Redundancy is controlled when the
DBMS ensures that multiple copies of the same data are consistent; for example, if a new
record with StudentNumber=8 is stored in the database of Figure 1.5(a), the DBMS will
ensure that StudentName=Smith in that record. If the DBMS has no control over this, we
have uncontrolled redundancy.

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