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Common exam pitfall
Students often confuse range checks (numerical limits) with length checks (number of characters).
Validation is an automatic computer check performed by software to ensure that data entered into a system is sensible, reasonable, and conforms to predefined rules before it is processed or committed to a database.
1. The Critical Distinction
Note: Exam Golden Rule: Validation DOES NOT check if data is factually correct. It only checks whether the data is acceptable according to the rules of the system. For example: If a student types their name as "Dvaid" instead of "David", a validation check will accept it because "Dvaid" satisfies presence, length, and character-type checks!
2. The Six Standard Validation Checks
Validation Check | Definition / Rule Tested | Concrete Example |
|---|---|---|
Range Check | Verifies that a numerical or date value falls between an upper and lower boundary. | Month must satisfy $1 \le \text{Month} \le 12$. Exam score $0 \le \text{Mark} \le 100$. |
Length Check | Verifies that a string contains either an exact number of characters or falls within minimum/maximum limits. | Password must be $\ge 8$ characters. PIN text must contain exactly 4 characters; a separate format check can require digits. |
Type Check | Verifies that the value has the expected data type. | Age must be an integer. A STRING type alone does not restrict a surname to letters; a separate format rule is needed. |
Presence Check | Verifies that a mandatory data field has not been left blank or empty. | National Insurance number or Email address field cannot be empty. |
Format Check | Verifies that text conforms to a specific pattern or character mask. | Postal code matching |
Check Digit | A calculated value appended to the end of a numerical code to detect transmission, transcription, or transposition errors. | Final digit of an ISBN-13 book code or EAN-13 barcode recalculated via modulo arithmetic. |
3. Implementing Validation in Cambridge Pseudocode
Input validation loops ensure incorrect entries are rejected immediately and re-prompted:
DECLARE StudentAge : INTEGER
REPEAT
OUTPUT "Enter student age (11 to 18): "
INPUT StudentAge
IF (StudentAge < 11) OR (StudentAge > 18) THEN
OUTPUT "Invalid age! Must be between 11 and 18."
ENDIF
UNTIL (StudentAge >= 11) AND (StudentAge <= 18)
OUTPUT "Valid age recorded: ", StudentAgeNotice that the REPEAT ... UNTIL loop checks the valid condition at the bottom to exit.
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Exam-Style Question: Classify Data Validation Checks
Identify the most appropriate validation check (Range check, Length check, Type check, or Presence check) for each requirement:
- Ensuring an examination percentage mark is between 0 and 100: [Space 1]
- Ensuring a postal code contains between 6 and 8 characters: [Space 2]
- Ensuring an age field contains numeric digits only and no alphabetic characters: [Space 3]
- Ensuring a mandatory email address input box is not left blank: [Space 4]
Interactive exercises for Module 2 and beyond require an active plan.