Why Requirements Engineering Is So Hard

From: dave.productmanager@yasco.com
To: karl.developer@yasco.com
Date: Fri, 13 Dec 2006 10:59:22 -0300
Subject: CustomerComany Inc.

Hey Karl,

we have a request from a customer that wants to place an order of some million dollars for our Xeepid. The customer now needs to know if it can fly. Can it?

Dave

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From: karl.developer@yasco.com
To: dave.productmanager@yasco.com
Date: Fri, 13 Dec 2006 10:59:26 -0300
Subject: Re: CustomerComany Inc.

Of course it can fly.

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From: greg.manager@bigcuco.com
To: fred.manager@yasco.com
Date: Mo, 7 Jan 2007 19:42:00 -0300
Subject: Xeepid

Dear Mr. Manager,

yesterday the first 2000 units of Xeepid arrived. Our development department started right away to integrate your Xeepid into our space ship. Unfortunately Xeepid didn't meet the requirements we asked for.
Mr. Productmanager told us that Xeepid could fly. IT CAN'T EVEN TAKE OFF! This is a serious fraud and we're going to sue you big time. Did you really think that you would get away with selling us an ordinary umbrella for our space ship project?

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Emergency Meeting, Meeting Room 42:
[ Fred Manager, Dave Productmanager, Karl Developer ]

Fred: "Um, we have a little problem with one of our best customers. You all got a copy of this e-mail, right? So, Dave, what was going on?"

Dave: "Yea, right, I just did what I always do. The customer asked us if Xeepid could fly, so I asked Karl - and Karl told me that it could fly. Did you get that copy of the e-Mail, Fred?"

Fred: "Um, right. So, Karl, tell us, why did you tell Dave that Xeepid could fly. I mean, it's just an umbrella - how far would you say an umbrella can fly?"

Karl: "Of course it can fly. Anything can fly, it's just a question of how much energy you put into the task."

Dave: "Oh, great, you developers are bright guys, can't you just think about what the customer wants for a moment."

Karl: "Why should I do your job?"

Fred: "Hey guys, calm down. Let's try to concentrate on how can we blame all this on the customer..."

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Today I tried to explain to my wife why requirements engineering is so hard. At first I just told her that you have to ask the customer what he wants. My wife said that it was obvious to her that you have to make sure you know what the customer wants. What is so difficult about asking the customer whether the product should fly?

The problem is: requirements engineering is not about the obvious questions. It's about asking the right questions to get requirements as unambiguous as possible. If a product should fly, you'd have to ask how far, at what speed, what type of fuel it should consume, how much fuel per mile it may use, or how it should be steered.

Every question leads to a myriad of new questions and all of them must be answered in the product. If a question is not asked, it may very well be perfectly what the customer wants - or not.

Asking the developers about features is a big challenge, since developers tend to think differently about the world than "normal" people. If you ask a developer how far an umbrella can fly, she will probably ask you how far you think you can throw it.