Feeds

Disintermangling use case scenarios from requirements

Yes, it is a word...

The Power of One eBook: 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.

HP ProLiant Gen8: Integrated lifecycle automation

More from The Register

next story
Whoah! How many Google Play apps want to read your texts?
Google's app permissions far too lax – security firm survey
Chrome browser has been DRAINING PC batteries for YEARS
Google is only now fixing ancient, energy-sapping bug
Do YOU work at Microsoft? Um. Are you SURE about that?
Nokia and marketing types first to get the bullet, says report
Microsoft takes on Chromebook with low-cost Windows laptops
Redmond's chief salesman: We're taking 'hard' decisions
EU dons gloves, pokes Google's deals with Android mobe makers
El Reg cops a squint at investigatory letters
Big Blue Apple: IBM to sell iPads, iPhones to enterprises
iOS/2 gear loaded with apps for big biz ... uh oh BlackBerry
OpenWRT gets native IPv6 slurping in major refresh
Also faster init and a new packages system
prev story

Whitepapers

Reducing security risks from open source software
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.
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.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Consolidation: the foundation for IT and business transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.