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GO Classes DPP | GATE CS, DA | DBMS | Update Anomaly

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1 1 vote

A relation contains four tuples for course $\text{CS 186}$, and every tuple stores the teacher as $\text{Hellerstein}$.

Lets consider the set of data is as follows :

\[
\begin{array}{|c|c|c|c|c|c|}
\hline
\text{Course} & \text{Teacher} & \text{Room} & \text{Hour} & \text{Student ID} & \text{Grade} \\
\hline
\text{CS 186} & \text{Hellerstein} & \text{Soda 306} & \text{12:30 TR} & \text{2154} & \text{A} \\
\hline
\text{CS 186} & \text{Hellerstein} & \text{Soda 306} & \text{12:30 TR} & \text{1129} & \text{A} \\
\hline
\text{CS 186} & \text{Hellerstein} & \text{Soda 306} & \text{12:30 TR} & \text{8510} & \text{AB} \\
\hline
\text{CS 186} & \text{Hellerstein} & \text{Soda 306} & \text{12:30 TR} & \text{4243} & \text{C} \\
\hline
\text{CS 286} & \text{Stonebraker} & \text{Cory 150} & \text{11:00 TR} & \text{9821} & \text{C} \\
\hline
\text{CS 286} & \text{Stonebraker} & \text{Cory 150} & \text{11:00 TR} & \text{8435} & \text{A} \\
\hline
\text{CS 286} & \text{Stonebraker} & \text{Cory 150} & \text{11:00 TR} & \text{2835} & \text{A} \\
\hline
\text{CS 150} & \text{Patterson} & \text{Soda 505} & \text{1:00 TRF} & \text{7235} & \text{AB} \\
\hline
\text{CS 150} & \text{Patterson} & \text{Soda 505} & \text{1:00 TRF} & \text{8510} & \text{AB} \\
\hline
\text{CS 150} & \text{Patterson} & \text{Soda 505} & \text{1:00 TRF} & \text{2449} & \text{AB} \\
\hline
\text{CS 170} & \text{Blum} & \text{Soda 405} & \text{2:25 MWF} & \text{9821} & \text{B} \\
\hline
\text{CS 170} & \text{Blum} & \text{Soda 405} & \text{2:25 MWF} & \text{8510} & \text{A} \\
\hline
\text{CS 170} & \text{Blum} & \text{Soda 405} & \text{2:25 MWF} & \text{2154} & \text{BC} \\
\hline
\end{array}
\]

Suppose the teacher changes to $\text{Garcia}$, but only three of the four tuples are updated.

What problem has occurred?

  1. Insertion anomaly
     
  2. Deletion anomaly
     
  3. Update anomaly
     
  4. No anomaly, because different tuples may store different teachers for the same course

1 Answer

1 1 vote

$\text{Teacher}$ information is stored repeatedly because several $\text{student}$ tuples correspond to the same $\text{course}$.

Initially, the relation contains repeated copies of the fact:

$\text{CS 186} \rightarrow \text{Hellerstein}$

If the teacher changes, every copy must be modified.

Suppose three rows become

$\text{CS 186} \rightarrow \text{Garcia}$

while one row still contains

$\text{CS 186} \rightarrow \text{Hellerstein}$

The database now represents two conflicting values for the same fact.

This inconsistency is caused by redundant storage and a partial update.

Therefore, this is an update anomaly.

Hence, the correct answer is C.

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