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Requirements Concepts

Confusion over product requirements terminology and concepts is pervasive. Companies are producing MRDs, PRDs, and SRSes without even understanding what "requirement" means. Despite this wasteful and unnecessary requirements document proliferation, companies are neglecting key nonfunctional requirements.

To help educate the product management and development community, I have put together a comprehensive model of concepts relating to requirements. To view or download the full-size conceptual model, click the image below:

(See my post on conceptual models if you have trouble understanding the diagram.)

A sampling of the terms that the conceptual model explicates:

  • functional requirement
  • nonfunctional requirement
  • attribute
  • constraint
  • metric
  • specification
  • condition
  • user
  • stakeholder
  • use case
You are free to distribute, copy, or print out the diagram, but please do not remove the copyright information on the bottom right.


Unknown said…
Where in your Requirements Concept would I identify my need/problem to reduce my operating costs and that by investing in a new application, say an ERP, I will achieve a Return on Investment such that my operating costs will be reduced by 30% within 2 years.
Roger L. Cauvin said…
Leonard, in the example, it sounds like excessive operating costs are the problem.

If the problem we commit to solving is

"Annual operating costs exceed x."

Then the requirement is

"Use of the product shall result in annual operating costs not to exceed x."

But in all likelihood we wouldn't commit to solving this problem. Instead, we would identify a lower-level set of problems such as:

"The amount of time spent planning resources exceeds x hours per month."


"The frequency of non-optimal resource planning decisions exceeds x per month."

Then the functional requirement would be:

"The product shall enable the user to plan resources."

And among the nonfunctional requirements would be:

"For users with profile y and resource profile z, the amount of time spent planning resources shall not exceed x hours per month."


"For users with profile y and resource profile z, the frequency of non-optimal resource planning decisions shall not exceed x per month."
Unknown said…
You might like to check out the BA BOK at I would describe your definition as a tailoring of the IIBA definition - which means it is made more useful for the situation you are in.
Roger L. Cauvin said…
Jules, thanks for pointing me to the BABoK document. The definition of "requirement" is essentially similar to the IEEE definition. The difference between my definition and the BABoK/IEEE definition is the insertion of the "least stringent" wording.

Without the "least stringent" part, virtually any condition - including detailed design specifications - could be requirements. See here for details.
yasodhara said…

I appreciate your analysis and formulation of statement of requirement.

This approach and conclusion are well defined in the TQM literature (7 methods 7 Tool of Quality Improvement). They are sound and applicable to most situations with a bit of tailoring or adaptation.

I particularly like

"Without the "least stringent" part, virtually any condition - including detailed design specifications - could be requirements."

This is the trap people fall into and get into endless arguments about there being no distinction between requirement and design. It is amazing how serious professionals of good standing plunge headlong into this.

Now about "requirement" the popular IEEE definition which is widely quoted is SRS which is more appropriately "System Capability Specification---NOT Business or User Need specification"

IEEE realized this mistake after decades of misapplication in 2011. Now the very basis of "requirement" specification by IIBA and IREB is knocked off. IIBA has a new definition based on their Core Concepts Model. IREB still sticks (without any justification) to the old IEEE definition which IEEE itself has discarded.

I have not recently checked what is the stand of BSC (UK based) on requirements. They were not in the spell of IEEE from what I recall.

So people may be more receptive to your definitions and explanations of requirements.

Best wishes,

Putcha V. Narasimham
Small correction:

Yasodhara used google account last on my notebook pc. So my previous message was attributed to her.

Anyway my name at the end of message indicates the real author.

Sorry for the error.

Putcha V. Narasimham
Roger L. Cauvin said…
Putcha, thanks for the interesting update on how the different organizations and standards bodies (IEEE, IIBA, IREB) have evolved their definitions of "requirement".

Can you point me to more information about the IEEE's 2011 change?

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