The table shown in Figure 1 is susceptible to update anomalies. Provide examples

Question

The table shown in Figure 1 is susceptible to update anomalies. Provide examples of insertion, deletion, and modification anomalies.

staffNo dentistName patientNo patientName appointment surgeryNo time S1011 S1011 S1024 S1024 S1032 S1032 Tony Smith Tony Smith Helen Pearson P108 Helen Pearson P108 Robin Plevin Robin Plevin Gillian White Jill Bell Ian MacKay Ian MacKay ill Bell John Walker ate 12-Aug-03 10.00 S10 13-Aug-03 12.00 S15 12-Sept-03 10.00 14-Sept-03 10.00 14-Oct-03 16.30 15-Oct-03 18.00 P100 P105 S10 S10 S15 S13 P105 P110 Figure 1: Details of patient dental appointments

Explanation / Answer

Update Anomaly:
If Patient P105's name is an error it must be updated at least 2 times or there will be inconsistent data in the database. If the user performing the update does not realize the data is stored redundantly, then the update will not be done properly.

Deletion anomaly:
A deletion anomaly is the unintended loss of data due to deletion of other data. For example, if doctor Robin Plevin needs to be removed, it will result in removal of patient John Walker from the system completely, which is not intended.

Insertion Anomaly:
An insertion anomaly is the inability to add data to the database due to absence of other data. For example, assume patientNo is defined so that null values are not allowed. Then in that case, Any new Doctor, who joins, can not be entered into the system without a patient. While, in real world, a doctor may not have any patients associated with it.

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