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Writing measurable non-functional requirements

A quality of a solution, such as speed, security or usability, written with a testable target, like a page loads in under 2 seconds, so you can check whether it is met.

Part of: VCE Applied Computing - U1O1 - Data analysis — Module 66, VCE Software Development - U3O1 - Programming — Module 3, VCE Software Development - U3O2 - Analysis and Design — Module 30, VCE Software Development - U4O2 - Cyber Security: secure software development practices — Module 73, VCE Data Analytics - U3O1 - Data Analytics — Module 4, VCE Data Analytics - U3O2 - Analysis and Design — Module 21, 9-10 Digital Technologies: Defining and decomposing problems — Module 17, VCE Applied Computing U1O2 Programming: Requirements and design tools — Module 3, QCE Digital Solutions Unit 1 — Understanding Digital Problems — Module 40, QCE Digital Solutions Unit 2 — Data-Driven Problems and Solution Requirements — Module 32, QCE Digital Solutions Unit 3 — Real-World Problems and Solution Requirements — Module 17, QCE Digital Solutions Unit 4 — Complex Digital Data Exchange Problems and Solution Requirements — Module 11

Understanding Writing measurable non-functional requirements in VCE Data Analysis

What it does: The success rate and time limit can be tested by watching new users try the task, so usability becomes measurable. A contrast ratio and alt text can be checked with tools, so accessibility can be tested rather than just described. A measurable requirement names a quality (performance) and a testable target (under 2 seconds). 'Really fast' can't be tested. 'Easy and fun' is an opinion. '3 taps or fewer' is a target you can test with real users. 'Hardly ever' is vague. A percentage of uptime gives a number you can check against logs. 'Strong security' names no test. Password length and lockout limits can be checked directly.

Common mistakes: 'Quickly' is vague and cannot be tested. A measurable requirement needs a target, such as 'Page loads in under 2 secs'. 'User friendly' has no testable target. It should be measurable, such as 'New user signs up in 3 min'.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

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This module's key terms are also in a printable crossword (Modules 56–67) and word search (Modules 56–80).

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Learning
Duo
Which non-functional requirement is measurable?
The app must load the home screen in under 2 seconds.The app must load really fast.
Matches
The app must be fast and easy to use.
↓
Words like 'fast' and 'easy' are vague opinions. There is no testable target, so you cannot check if the requirement is met.
Applying
Meanings
Term
measurable non-functional requirement
Meaning
A quality of a solution, such as speed, security or usability, written with a testable target, like a page loads in under 2 seconds, so you can check whether it is met.
Practice
Performance: The app loads in under 2 seconds.
Testing
Gaps
Performance: a page loads 2 seconds
Check Answer
Spots
1Performance requirement:
2Page loads quickly

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Quick Questions

1. Which non-functional requirement is measurable?
A. The app must load really fast.
B. The app must load the home screen in under 2 seconds. ✓
A measurable requirement names a quality (performance) and a testable target (under 2 seconds). 'Really fast' can't be tested.
2. Which usability requirement is measurable?
A. A new user can book a ticket in 3 taps or fewer, without help. ✓
B. The app must be easy and fun to use.
'Easy and fun' is an opinion. '3 taps or fewer' is a target you can test with real users.
3. Which reliability requirement is measurable?
A. The website must hardly ever crash.
B. The website must be available 99.9% of the time each month. ✓
'Hardly ever' is vague. A percentage of uptime gives a number you can check against logs.
4. Which security requirement is measurable?
A. Passwords must be at least 12 characters and locked after 5 failed log-in attempts. ✓
B. The system must have strong security.
'Strong security' names no test. Password length and lockout limits can be checked directly.
5. Which accessibility requirement is measurable?
A. All images must have alt text and text must have a contrast ratio of at least 4.5:1. ✓
B. The site must be accessible to everyone.
'Accessible to everyone' is a goal, not a test. Alt text and a contrast ratio can be checked with a tool.

Match the Pairs

The app must load each screen in under 2 seconds on a standard school Wi-Fi connection. → A measurable performance requirement: it names a quality (speed) and a testable target (under 2 seconds).
The system must be available 99.5% of the time during school hours, Monday to Friday. → A measurable reliability requirement: it names a quality (uptime) and a testable target (99.5%).
A measurable usability requirement gives a number that can be tested with real users. → At least 9 out of 10 new users must be able to book a tutor in under 3 minutes without help.
A measurable accessibility requirement names a recognised standard or checkable feature. → All text must have a colour contrast ratio of at least 4.5:1 and every image must have alt text.
The app must be fast and easy to use. → Words like 'fast' and 'easy' are vague opinions. There is no testable target, so you cannot check if the requirement is met.
The system must keep user data very secure. → 'Very secure' has no testable target, so nobody can check whether it has been achieved.

Key Term

measurable non-functional requirement
A quality of a solution, such as speed, security or usability, written with a testable target, like a page loads in under 2 seconds, so you can check whether it is met.

Fill in the Blanks

1. Performance: a page loads under 2 seconds
Hint: Type the word that sets the upper time limit for the target.
2. Reliability: the app is up 99.9% of the time
Hint: Type the name of the quality about how dependable the system is.
3. Usability: users sign up in under 2 minutes
Hint: Type the unit of time that makes the target testable.
4. Security: login locks after 3 failed attempts
Hint: Type the word describing the unsuccessful login tries that are counted.
5. Accessibility: 100% of images have alt text
Hint: Type the short name for the text description that helps screen reader users.

Spot the Error

Question 1
A Performance requirement:
B Page loads quickly
C Search returns in under 1 sec
Line B — 'Quickly' is vague and cannot be tested. A measurable requirement needs a target, such as 'Page loads in under 2 secs'.
Question 2
A Usability requirement:
B Sign-up must be user friendly
C Menu is reached in 2 taps
Line B — 'User friendly' has no testable target. It should be measurable, such as 'New user signs up in 3 min'.
Question 3
A Reliability requirement:
B The app should never fail
C Crashes under 1 per month
Line B — 'Never fail' is not a testable target. Reliability needs a measurable figure, such as 'Uptime is at least 99.5%'.
Question 4
A Passwords must be very secure
B Lock after 5 failed logins
C Log out after 10 min idle
Line A — 'Very secure' cannot be checked. A security requirement needs a target, such as 'Passwords need 8+ characters'.
Question 5
A Accessibility requirement:
B Text can be resized to 200%
C Text is easy to read for all
Line C — 'Easy to read for all' is vague. An accessibility requirement needs a testable target, such as 'Text contrast ratio is 4.5:1'.

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