Here are a few examples of how the data in a database may become invalid if proper checks are not made. You can prevent each of these examples from occurring using facilities described in this chapter.
An operator types the date of a sales transaction incorrectly.
An employee's salary becomes ten times too small because the operator missed a digit.
Two different people add the same new department (with DepartmentID 200) to the Departments table of the organization's database.
The department identified by DepartmentID 300 closes down and one employee record inadvertently remains unassigned to a new department.