Provide examples of insertion, deletion, and modification anomalies PLEASE TYPE
ID: 3739469 • Letter: P
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Provide examples of insertion, deletion, and modification anomalies
PLEASE TYPE THE ANSWER.. NO PHOTO OR SCAN
staffNo dentistName patientNo patientName surgeryNo appointment date 12-Aug-03 10.00 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 time S10 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 Jill Bell John Walker P100 P105 S10 S10 S15 S13 P105 P110 Figure 1: Details of patient dental appointments.Explanation / Answer
Anomalies
Anomalies usually occur in database systems when the tables are not normalized. These can insertion, modification and deletion anomaly.
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Insertion anomaly occurs when one is unable to insert data until all the attributes have data. For example, consider an employee table with columns empid, name, department columns . Suppose the department column is defined as not null, one will not be able to insert a row for an employee that is not yet linked to a department.
In the given table "patient number & patient name" is defined as not null then it wouldn't be possible to insert a staff details,who doesn't have any patient associated.Such situations prevent the data insertions,until all attributes are valued causes insertion anomaly.
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An update anomaly occurs when there are multiple rows that need an update but updates happen only on certain rows creating data inconsistencies in the database. In the same example mentioned above, when an employee is linked with multiple departments and an update to the name was made only to a single row, it causes update anomaly.
From the given table ,If there is a change in the name of the dentist,"Tony Smith",an update to be done on two rows of the table.Failure of updating the 2 rows will result in database inconsistency.This is called update anomaly.
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A delete anomaly occurs when a deletion does not happen on all relevant rows leaving inconsistencies to the database. For example,
If we delete the dentist name "Tony Smith",this result in the complete deletion of the patient "P100" from the table.Such unintended lose of data because of removal of another data is called deletion anomaly
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