Validation & Verification

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Notes

Validation & Verification Overview

**Validation** is an automated process checking if input is sensible and meets program requirements.
**Verification** checks that data entered matches the original intended data (accuracy).
Validation ensures data is possible/reasonable; verification ensures it is correct.

Types of Validation Checks

**Range check**: ensures a number falls within a specified range (e.g., 0–100).
**Length check**: ensures a string has a required number of characters (e.g., PIN = 4 digits).
**Type check**: ensures data is of the correct data type (e.g., integer, string).
**Presence check**: ensures a field is not left blank.
**Format check**: ensures data matches a pattern (e.g., XX9999, email with @ and .).
**Check digit**: a final digit calculated by algorithm to detect errors in codes (e.g., ISBN).

Verification Methods

**Double entry**: data entered twice; system compares both entries; mismatch triggers error.
**Visual check**: user reviews data on screen and confirms correctness (e.g., popup).
Example: password confirmation uses double entry; name entry uses visual check.

Suitable Test Data Categories

**Normal data**: valid input that should be accepted (e.g., age 16 for range 12–18).
**Abnormal data**: invalid data type or value that should be rejected (e.g., 'H' for age).
**Extreme data**: boundary values that are still acceptable (e.g., 12 and 18).
**Boundary data**: values just inside and just outside the acceptable range (e.g., 11, 19).

Trace Tables

A **trace table** records the state of variables and outputs at each step of an algorithm.
Used to detect logic errors in flowcharts, pseudocode, or program code.
Each row corresponds to one step/iteration; columns for inputs, outputs, and variables.
Helps discover the purpose of an algorithm by showing intermediate results.

Validation checks act like a series of gates; data must pass each check to be accepted.

Flowchart showing how data passes through validation and verification before acceptance.

Test data categories: each type of data tests a different aspect of the program.

Practice questions

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1.What is the purpose of validation?
Easy
- ATo check that data entered is sensible and meets program requirements
- BTo check that data entered is exactly what was intended
- CTo check that data is stored correctly in the database
- DTo check that data is transmitted without errors
2.A program asks the user to enter a password. Which two validation checks would be most appropriate for a password field?
Medium
- ALength check and presence check
- BRange check and type check
- CFormat check and check digit
- DPresence check and range check
3.A program uses the following pseudocode to validate input: REPEAT INPUT Number IF Number < 0 OR Number > 100 THEN OUTPUT "Invalid" ENDIF UNTIL Number ≥ 0 AND Number ≤ 100 Which type of validation is being performed?
Hard
- ARange check
- BLength check
- CType check
- DPresence check
4.Which of the following is an example of verification?
Easy
- ADouble entry checking
- BRange check
- CFormat check
- DCheck digit
5.A website registration form asks users to enter their email address twice. This is an example of:
Medium
- AVerification using double entry
- BValidation using format check
- CValidation using presence check
- DVerification using visual check
6.An ISBN number ends with a check digit. What is the purpose of the check digit?
Hard
- ATo help detect errors when the number is entered or transmitted
- BTo ensure the number is in the correct format
- CTo verify that the number belongs to a valid book
- DTo encrypt the number for security
7.Which validation check would reject the input "ABC" for an age field?
Easy
- AType check
- BRange check
- CLength check
- DPresence check
8.A program checks that a username is not left blank. Which validation check is this?
Medium
- APresence check
- BLength check
- CType check
- DFormat check

Slides

Validation & Verification

Validation is an automated process that checks if user input is sensible and meets program requirements.
Verification checks that data entered matches the original intended data.
Both are used to improve data quality during data entry.

Six Types of Validation

Range check: ensures a number falls within a specified range (e.g., 0–100).
Length check: checks the length of a string (e.g., PIN must be 4 digits).
Type check: verifies the data type (e.g., integer, string).
Presence check: ensures a field is not left blank.
Format check: validates the pattern of data (e.g., email must contain @ and .).
Check digit: a final digit calculated from the rest of the code (e.g., ISBN).

Which validation check would ensure a user enters a number between 1 and 100?

Range check
Length check
Type check
Presence check

Verification Methods

Double entry: data is entered twice and compared; if they don't match, an error is shown.
Visual check: the user reviews the data on screen and confirms it is correct.

Which verification method involves entering data twice and comparing?

Visual check
Double entry
Range check
Presence check

Suitable Test Data

Normal data: values that should be accepted (e.g., age 16 for a 12–18 range).
Abnormal data: values of the wrong type (e.g., entering 'H' for age).
Extreme data: the minimum and maximum acceptable values (e.g., 12 and 18).
Boundary data: values just above and below the limits (e.g., 11 and 19).

For a program that accepts ages between 12 and 18 inclusive, which is an example of extreme data?

Trace Tables

A trace table is used to test algorithms for logic errors by recording variable values at each step.
It can be used with flowcharts, pseudocode, or program code.
Each iteration or step is executed and the state of inputs, outputs, and variables is recorded.

A trace table records the state of ____ at each step of an algorithm.

Trace Table Example

Consider an algorithm that finds the highest of ten numbers.
The trace table has columns for Count, Highest, Number, and Output.
Each row shows the state after processing one input number.

Which of these are true about validation?

Validation checks if data is sensible and meets requirements.
A length check ensures a number is within a range.
A presence check ensures a field is not left blank.
Verification and validation mean the same thing.

Check Digits

A check digit is a numerical value calculated from the other digits in a code (e.g., barcode, ISBN).
It is appended to the code and used to detect errors when the code is entered.
If the check digit does not match the recalculated value, an error is flagged.

What is the purpose of a check digit?

To ensure data is not left blank
To verify the data type
To detect errors in data entry
To check the length of a string

Difference Between Validation and Verification

Validation checks if data is reasonable/possible (e.g., age between 0 and 150).
Verification checks if data matches the original source (e.g., re-typing a password).
Validation is automated; verification may involve user action.

____ checks if data is sensible, while ____ checks if data is accurate.

Selecting Test Data

Test data should cover normal, abnormal, extreme, and boundary cases.
For a price check (< $10.00): 9.99 is normal/extreme/boundary (accepted), 10.00 is boundary (rejected), 'ten' is abnormal (rejected).
Expected outputs are compared with actual results to find errors.

For a program that accepts prices less than $10.00, what type of test data is 'ten'?

Normal
Extreme
Boundary
Abnormal

Using Trace Tables to Debug

Trace tables help identify logic errors by showing the exact sequence of operations.
They are especially useful for loops and conditional statements.
By comparing expected and actual values, programmers can locate bugs.

Which statements about trace tables are correct?

Trace tables can be used with flowcharts and pseudocode.
Trace tables record only the final output.
Trace tables help find logic errors.
Trace tables are only for testing validation checks.

Lesson Summary

Validation: range, length, type, presence, format, check digit.
Verification: double entry and visual checks.
Test data: normal, abnormal, extreme, boundary.
Trace tables: step-by-step record of variable values to debug algorithms.

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