Validation checker
Type a value and see which validation checks it passes — then find the wrong-but-valid entry that every check lets through.
- Validation checks
- Verification
- Why the two are different
Student age field
Presence check
The field is not left blank.
Type check
The data is the right kind — digits only for an age.
Range check
The value lies between 11 and 18 inclusive.
Length check
The entry is 1 or 2 characters long.
Every validation check passes — but the computer still has no idea whether this is actually this student's age. Only verification can tell you that.
Checks passed
4 / 4
Accepted by the system
yes
Verified as correct
unknown
Predict
A student aged 14 types 17 by mistake. Which check catches the error?
Experiment
- 1Type 15 and confirm every check passes.
- 2Try 9 and 150 and note that only the range check fails — the others cannot tell.
- 3Type abc and see the type check and range check both fail.
- 4Leave the field blank and identify which check exists precisely for that case.
Explain
Validation is an automatic check by the computer that the data entered is reasonable — the right type, within range, present, the right length or the right format.
Verification is a check that the data was entered accurately, matching the original source. The two methods are double entry, where the data is typed twice and the computer compares the copies, and a visual check, where a person proofreads the entry against the original document.
The distinction is worth marks in nearly every series, and the reason is exactly what this simulation shows: no validation check can tell a correct age from a plausible wrong one.