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.
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.