Feeds

Disintermangling use case scenarios from requirements

Yes, it is a word...

The Power of One Brief: Top reasons to choose HP BladeSystem

It turns out that my co-author Doug Rosenberg has a few things to say on the subject of use case style. So this week I'm going to leap in the back of the Dodge Ram pick-up truck and let him drive.

Over to Doug:

There's often a fair bit of confusion in the early stages of a software project about what exactly needs to be built, Doug says. So it's worthwhile investing some effort in getting to a point of clarity about the requirements before leaping into construction.

One of the chief points of confusion is the mangling-up of "active voice stuff" with passive voice stuff. Scenarios (or stories) are "active voice stuff", e.g. "the user clicks the cancel button and the system erases the disk".

In the UML universe, we call the active voice stuff (which describes runtime behaviour) "use case scenario text" and the passive voice stuff "functional requirements".

It's useful to separate the scenarios from the functional requirements, not least because you must understand the runtime behaviour unambiguously before you code the system - and this is much harder to do when it's "intermangled" with the functional requirements.

At ICONIX, we often work with projects that are contractually required to demonstrate compliance against a formal, written set of requirements - banking systems, aerospace/defence projects, etc, and we've run into this "intermangling" phenomenon more times than we'd like to recall.

Here's an example: Once, when I walked into a client's building to conduct a training workshop, I was handed a hefty use case document. As I flipped through the use cases, I noticed that the scenario text was interspersed with lines that started with [REQUIREMENT]. So there would be a couple of lines of active voice scenario stuff, followed by a couple of lines of [REQUIREMENT]s, and so on.

Several of these uniquely numbered [REQUIREMENT]s were repeated on multiple pages (all with unique numbers, of course). So I took a deep breath and had the following conversation:

DOUG: It looks like some of these functional requirements repeat across several use cases...

CLIENT: Oh definitely! Some of them are in there 70 or 80 times.

DOUG: Oh... (silently emits "primal scream")

DOUG: Pauses (looking calm while still screaming silently)

DOUG: And they all seem to be uniquely numbered...

CLIENT: (brightly) Yep!

DOUG: So... how do you know whether you have 320 distinct requirements, or four requirements repeated 80 times each?

CLIENT: (smiling) Don't know... never thought about that one.

DOUG: What did you say your name was?

I had recently returned from teaching another class in Texas, where they're fond of taking liberties with the English language. Thus, the word "disintermangling" was born.

I'll wrap up with this thought: Unambiguous scenario descriptions are key to understanding what you're building before you code it. But before you can disambiguate the scenarios, you need to disintermangle them from the functional requirements.

Doug Rosenberg is an author and noted OO instructor, and runs public training classes worldwide.

Seven Steps to Software Security

More from The Register

next story
KDE releases ice-cream coloured Plasma 5 just in time for summer
Melty but refreshing - popular rival to Mint's Cinnamon's still a work in progress
NO MORE ALL CAPS and other pleasures of Visual Studio 14
Unpicking a packed preview that breaks down ASP.NET
Secure microkernel that uses maths to be 'bug free' goes open source
Hacker-repelling, drone-protecting code will soon be yours to tweak as you see fit
Cheer up, Nokia fans. It can start making mobes again in 18 months
The real winner of the Nokia sale is *drumroll* ... Nokia
Put down that Oracle database patch: It could cost $23,000 per CPU
On-by-default INMEMORY tech a boon for developers ... as long as they can afford it
Another day, another Firefox: Version 31 is upon us ALREADY
Web devs, Mozilla really wants you to like this one
Google shows off new Chrome OS look
Athena springs full-grown from Chromium project's head
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Consolidation: The Foundation for IT Business Transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.
Application security programs and practises
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
How modern custom applications can spur business growth
Learn how to create, deploy and manage custom applications without consuming or expanding the need for scarce, expensive IT resources.
Securing Web Applications Made Simple and Scalable
Learn how automated security testing can provide a simple and scalable way to protect your web applications.