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What data validation is and why it matters

An automatic check that data is reasonable and allowed when it is entered, such as being in range or the right type, so typos and impossible values are caught.

Part of: VCE Applied Computing - U1O1 - Data analysis — Module 29, 7-8 Digital Technologies: Acquiring, storing and validating data — Module 12, WA Computer Science ATAR Year 11 — Data Management — Module 54

Understanding What data validation is and why it matters in VCE Spreadsheets, SQL & Visualisation

What it does: A range rule is a type of validation that rejects values outside what is sensible. If invalid data gets in, results like averages are unreliable, which is why validation matters. Validation checks that a value is reasonable, not just that it is a number. 250 is an impossible age, so it should be caught. If the data entered is wrong, any charts, totals or answers made from it will be wrong too. Validation helps stop bad data getting in. A type check makes sure the data is the right kind, such as a number instead of text. Validation works at the moment of entry, so mistakes are caught straight away before they spoil the data.

Common mistakes: The minimum age for the range check is 11. Setting it to 19 makes the minimum bigger than the maximum, so every age would be rejected. It should be min ← 11. Validation should show the error message when the score is NOT a number. As written, it complains about correct data. It should be IF score is not a number.

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This module's key terms are also in a printable crossword (Modules 21–34) and word search (Modules 4–34).

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Learning
Duo
Which best describes data validation?
An automatic check that data entered is reasonable and allowedMaking sure the data is true by asking someone else
Matches
Height (cm): 1750 accepted, because the cell has no validation
↓
Without validation, a typo like 1750 instead of 175 is accepted. A range check would have rejected it.
Applying
Meanings
Term
validation
Meaning
An automatic check that data is reasonable and allowed when it is entered, such as being in range or the right type, so typos and impossible values are caught.
Practice
INPUT age
Testing
Gaps
IF age < 0 age > 120 THEN
Check Answer
Spots
1min ← 19
2max ← 18

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Quick Questions

1. Which best describes data validation?
A. An automatic check that data entered is reasonable and allowed ✓
B. Making sure the data is true by asking someone else
Validation is done by the computer as data is entered. It checks the data follows rules, such as being in range or the right type.
2. A student types 250 into an Age cell for a Year 7 class. What should validation do?
A. Accept it because 250 is a number
B. Reject it because 250 is an impossible age ✓
Validation checks that a value is reasonable, not just that it is a number. 250 is an impossible age, so it should be caught.
3. Which is an example of a validation check?
A. Only allowing scores between 0 and 100 ✓
B. Sorting scores from highest to lowest
A range check is a type of validation. Sorting only changes the order of the data and does not check it.
4. What does 'garbage in, garbage out' mean?
A. Deleting old data makes a spreadsheet faster
B. Bad data going in gives bad results coming out ✓
If the data entered is wrong, any charts, totals or answers made from it will be wrong too. Validation helps stop bad data getting in.
5. Which is the difference between validation and verification?
A. Validation checks data is reasonable; verification checks it matches the original source ✓
B. Validation checks it matches the original source; verification checks it is in range
Validation asks 'is this allowed and sensible?'. Verification asks 'is this exactly what the source said?'. A value can pass validation and still be a wrong typo.

Match the Pairs

validation → An automatic check that data is reasonable and allowed when it is entered, like being in range or the right type
verification → Checking that data matches the original source, such as re-reading what you typed against the survey form
Validation catches an impossible value, like a student age of 150 when the allowed range is 11 to 14 → Age must be between 11 and 14
Garbage in, garbage out means bad data entered gives bad results, so validation helps keep it clean → Typed 'abc' into a Score field -> average is wrong
Height (cm): 1750 accepted, because the cell has no validation → Without validation, a typo like 1750 instead of 175 is accepted. A range check would have rejected it.
Validation proves 'Jorda' is the correct spelling of the student's name Jordan → Validation only checks data is reasonable and allowed, not that it is correct. Verification against the source is needed to catch this typo.

Key Term

validation
An automatic check that data is reasonable and allowed when it is entered, such as being in range or the right type, so typos and impossible values are caught.

Fill in the Blanks

1. IF age < 0 OR age > 120 THEN DISPLAY "Invalid age" END IF
Hint: Type the logical operator that rejects the age if either impossible condition is true.
2. =IF(AND(B2>=0,B2<=100),"OK","Check")
Hint: Type the function that is only true when both range conditions are met.
3. REPEAT INPUT score UNTIL score >= 0 AND score <= 100
Hint: Type the keyword that keeps asking for input until the entered value passes the validation check.
4. IF NOT ISNUMBER(age) THEN DISPLAY "Enter a number" END IF
Hint: Type the function name that checks whether the data is the right type.
5. IF mark > 100 THEN DISPLAY "Mark is impossible" END IF
Hint: Type the comparison operator that catches a mark above the maximum allowed.

Spot the Error

Question 1
A min ← 19
B max ← 18
C INPUT age
D IF age < min OR age > max
E SHOW 'Out of range'
Line A — The minimum age for the range check is 11. Setting it to 19 makes the minimum bigger than the maximum, so every age would be rejected. It should be min ← 11.
Question 2
A INPUT score
B IF score is a number
C SHOW 'Numbers only'
Line B — Validation should show the error message when the score is NOT a number. As written, it complains about correct data. It should be IF score is not a number.
Question 3
A INPUT height
B IF height > 0 AND height < 250
C REJECT height
D ELSE
E REJECT height
Line C — When the height passes the range check, it is reasonable data and should be accepted. Rejecting it here is wrong. It should be ACCEPT height.
Question 4
A INPUT email1
B INPUT email1
C IF email1 = email2
D SHOW 'Email confirmed'
Line B — Verification asks the user to enter the data twice and compares the two entries. The second entry must go into email2. If both are stored in email1, the check is always true and verifies nothing.
Question 5
A INPUT mark
B IF mark < 0 OR mark > 100
C SHOW 'Mark must be 0-100'
D ACCEPT mark
E ELSE
F ACCEPT mark
Line D — An impossible mark such as 150 must be rejected after the error message is shown. Accepting it lets bad data in. Line 4 should be REJECT mark.

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