Validation: range, type, length and presence checks

Overview

Data validation, range check and type check.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Define data validation.

   Model answer

   Data validation is an automatic check carried out by a program on data as it is entered, confirming that the data is sensible and obeys the rules set for that field.

2. 2

   Why can validation not guarantee that data is correct?

   Model answer

   Validation tests only whether a value is allowable, so a wrong value that happens to obey the rules, such as an incorrect date of birth within the permitted range, is accepted without question.

3. 3

   What is a range check?

   Model answer

   A range check confirms that a numeric or date value falls between a stated lower limit and a stated upper limit.

4. 4

   Which range check suits a field holding the month of a date as a number?

   Model answer

   A month number should be checked to be no less than 1 and no greater than 12.

5. 5

   Which range check suits a field holding an examination mark expressed as a percentage?

   Model answer

   A percentage mark should be checked to lie between 0 and 100 inclusive.

6. 6

   A range check on a customer's age accepts any value from 0 to 120. Explain the weakness of this check.

   Model answer

   An age of 7 typed for a customer who is really 70 falls inside the permitted range and is accepted, so the check catches only impossible ages and not mistaken ones.

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