The phone that does everything, badly

A new phone can call, text, play music and take photos. It does everything a phone must do.

But each app takes 10 seconds to open, the battery lasts one hour, and anybody can unlock it.

Would you buy it? No. It does the job, but badly. A requirement is something the software must do or be. Some are about how well the software must work. They are called non-functional requirements.

Key words

Word	What it means	Example
Functional requirement	Something the software must DO.	send a receipt
Non-functional requirement	How well the software must work.	send it in 5 seconds
Scalability	How well the software works when it gets bigger.	500 users now, 50,000 later
Accessibility	Making software usable by people with different needs.	a text description for people who cannot see the picture
KPI	A number that shows if the software is doing well enough.	a page loads in 2 seconds
Metric	Something you can measure, in numbers.	milliseconds, users, minutes
Millisecond	A very short time. 1,000 milliseconds is 1 second.	2,000 milliseconds is 2 seconds
Acceptance criteria	Checks that must pass before the client accepts the work.	The receipt arrives by email.
Spike	A short, time-limited piece of research or trial to learn something.	2 days to test a new service

The cells students fill in are left blank in this preview.

Kinds of non-functional requirement

Kind	The question	Example with a number
Security	Who can get in or see data?	Accounts lock after 5 wrong passwords
Accessibility	Who can use it?	All text can be made twice as big
Scalability	Does it still work when there are many more users?	Works for 500 users now and 5,000 next year
Responsiveness	How quick is it?	A page answers in 2 seconds or less
Load handling	How many at once?	Works for 500 users at the same time
Reliability	How often is it not working?	Down (not working) for no more than 45 minutes a month

The cells students fill in are left blank in this preview.