Validation and verification checks

Hello students, welcome to Kwickprep. On an admission form, a student types her age as 150. Should the computer accept it? Today we will learn the validation checks and verification checks that stop bad data from entering a system.

These two words sound alike, so let us separate them first. Validation is an automatic check by the program that data is sensible and follows the rules. Verification checks that data was copied or typed exactly as in the original. It is done by entering the data twice or by checking it with your eyes.

Here is a key exam point. Validation only checks that data is reasonable. It cannot prove the data is actually correct. If a student is fifteen but types fifty one, a range check from zero to one hundred and twenty still accepts it. That is why we also need verification.

Here are the six validation checks you must know. A range check tests that a value lies between a lower and an upper limit, like marks from zero to one hundred. A length check tests the number of characters, like an Indian PIN code having exactly six digits. A type check tests the data type, like age being a whole number. A presence check makes sure a field is not left empty. A format check tests a pattern, like a date written as day, month and year. A check digit is an extra digit calculated from the other digits, used on book numbers and barcodes.

Here is a range check in Python. The word or means the condition is True if either part is True. Marks is one hundred and five, which is more than one hundred. So the program prints Out of range. Notice that zero and one hundred themselves are accepted.

This program does two checks on a PIN code. First, a presence check: two quote marks with nothing inside mean an empty string, so nothing was typed. Next, a length check: len gives the number of characters. This PIN has only five characters, and not equal to six is True. So it prints PIN must be six digits.

Now a type check. Typed input arrives as text, so we test whether every character is a digit. The method is digit returns True only when all characters are digits. Here the student typed one and the letter a by mistake. So it prints Age must be a number.

A check digit is worked out from the other digits and added to the end of the code. Here is a very simple made up rule: add the digits and keep the last digit of the sum. Nine plus seven plus eight plus four is twenty eight. Twenty eight modulus ten, the remainder after dividing by ten, is eight. If a digit is typed wrongly, the check digit will usually not match. Real ISBN and barcode rules use weights, but the idea is the same.

In exams you often write a validation loop in pseudocode. The repeat loop asks for a mark. It keeps asking until the mark is between zero and one hundred. So the program never moves on with an invalid mark.

Now verification, which has two methods for data entry. In double entry, the data is typed in twice, like a new password. The computer compares the two entries and rejects them if they differ. In a visual check, the person looks at the data on the screen and compares it with the original document. This is done by a person reading carefully, so it can still miss errors.

Here is double entry for a new password. The user types the password twice, and the program compares them with double equals. The second entry has the last two digits swapped. The entries are different, so it prints Entries do not match. A validation check alone could not catch this.

Pause and predict. A range check accepts marks from zero to one hundred, including both ends. A student enters exactly one hundred. Is it accepted or rejected? It is accepted, because one hundred is one of the limits and the limits are included.

Let us match situations to checks. A mobile number with only nine digits fails a length check. An empty email box fails a presence check. A price typed as letters fails a type check. When a clerk copies a bank code from a form, a visual check against the form verifies it.

Let us revise what we learned today. Validation checks that data is sensible, and the program does it automatically. The six checks are range, length, type, presence, format and check digit. Verification checks that data was copied correctly. Its two methods are double entry and a visual check. Remember, validation cannot prove that data is correct.