Home Work 1



HW 1

Solution

The file shown in Fig 1-5 has five problems 1. uncontrolled data redundancy 2. delete anomaly 3. insert anomaly 4. update anomaly, and 5. data inconsistency.

1. Uncontrolled Data redundancy

There are several examples of uncontrolled data redundancy. Uncontrolled Data redundancy occurs when the same data are unnecessarily stored in several places in the same file. For example, there are three records (rows 1, 2, 3) that contain the name of the hurricane project and the same could be said for the records containing coast and satellite projects.

2. Delete anomaly

A delete anomaly occurs when you delete a record other important information is lost. For example, if the coast project were to be deleted, employee info about Newsome and Ramoras working on the coast project would be lost and we would have no future record of that fact.

3. Insert anomaly

An insert anomaly occurs when you are forced to add dummy info to columns or leave them blank. For example, if a new project was added, we would be forced to add info about employees that are not assigned to the project at the moment. The other alternative is to leave the employee and job fields blank thus creating nulls. Having null values in a table is not a good idea.

4. Update anomaly

An update anomaly occurs when you are forced to make unnecessary changes to data that reside in the same file. For example, if the hurricane project name changed, we would have to change it in three places.

5. Data inconsistency

Clerical errors caused by uncontrolled data redundancy leads to data inconsistency. For example, job-charge-hr for the same job has two different values, $26 and $62, and the project name satellite is misspelled.

NOTE:

I told you how many problems there are.

I gave you a clear definition of each problem.

I gave you an example of each problem from the table in question.

I provided a pic from SQL that meets the guidelines specified in the syllabus.

[pic]

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