1 Discuss any scenario where an entity can be classified as

1. Discuss any scenario where an entity can be classified as a weak entity.

2. What two conditions must be met before an entity can be classified as a weak entity? Give an example of a weak entity.

3. How the insertion, deletion and modification actions create the problems in the unnormalized table.

Solution

1.

A weak entity depends on strong entity for its existence.

Example

2.

Conditions that must be met before an entity can be classified as a weak entity.

3.

Insertion,deletion and modification anomalies in unnormalized table.

Consider an unnormalized table Employee_Department(EmpNumber,EmpName,Address,Salary,DepartmentNumber,DepartmentName,DepartmentManager)

Insertion anomaly

If the company wants to create a new Department but there are no employees . So we have to insert null in EmpNumber which is primary key and this is not possible. We are having an insertion anomaly.

Deletion anomaly

If an Employee quits the company , his details should be deleted . So the corresponding details of Department will also get deleted. If there is only single employee in a department, that department details will also get deleted which is not required. So we are having a deletion anomaly.

Modification anomaly

If the manager of a department changes,so DepartmentManager should be updated for all rows corresponding to that DepartmentNumber. But if we fail to do so, there will be inconsistency in the database. This is modification anomaly.

We can remove all these anomalies by normalizing tables as follows