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New Post 6/17/2013 8:48 AM
User is offline JD
1 posts
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Functional Requirements definition dilemma 


I'm new to this forum so I'll start by a brief introduction of myself and of my current situation.


I've been working as a tester in the video game industry for 5 years, then I moved to the medical software as a quality assurance analyst for 2 years. During those 2 years, I've been able to identify the root cause of most issues we had. No clear requirements. The solution they found is naming me the official functional analyst/designer.


Now that I'm in charge of requirements management and definition, I'm trying to figure out how to write functional requirements (since we already have some high level User Requirements).


Some books and articles define functional requirement like this: "System provides or does something", while others define it more like: "[Trigger] Actor does Action on Object [Conditions]".

Multiple definitions can also be found over the internet. One even compare the functional requirement to a mathematical functions like "y = f(x)(1)" where Y will always be the same for the same X. In that case, I have to define each possible input and output for a function. Since most complex software rarely use a single input to procude a single output depending on different states, I have to handle this with input sets, output sets like this: {y}, {FS} = f({x}, {IS})(2), where {IS} and {FS} are initial state and final state respectively.

In the later, if a functional requirement statement must include all those components, we are far from the "The system shall do this".


Considering that those functional requirements will be used by developers to implement a feature, by designer to create the interface and by testers to create test cases, what would be the best approach to write complete but not over-detailed functional requirements ?

If any of you had to write functional requirements at one point, just letting me know how you wrote them might help me a lot!

Thank you!



New Post 6/18/2013 5:12 AM
User is offline Tony Markos
493 posts
5th Level Poster

Re: Functional Requirements definition dilemma 


I have been doing Business Analysis since the  early 80's.  I have seen alot.   I have never seen a WRITTEN functional spec that was of much use.   There are a number of reasons why this is so.   Writings about the Agile method talk about many of them.   Written functional specs are a big reason why alot of Agile proponents say that BA's are a waste of money.

Agile is about minimal, yet quality requirements.  (Alot of Agile folks think it means no documentation at all; don't be mislead by this false notition.)    The real thrust of Agile is being LEAN.   And, actually, lean can be done on any project - not just those that are labled "Agile".     My lean approach:  Some Data Flow Diagrams, a few ERD's, and maybe some screen shots is often all that is required.   The details of requirements can be handled in conversations between the developers.


New Post 6/22/2013 2:22 AM
User is offline Kimbo
454 posts
5th Level Poster

Re: Functional Requirements definition dilemma 

Hi JD,

If you already have your "the system shall..." type requirements than using UML and Use Cases with BPMN for process will do the job. Agile User Stories are just another version of Use Cases without the rigour IMHO.

Lotsa books out there if you aren't familiar with the techniques. I like:

Writing Effective Use Cases by Alistair Cockburn

UML Distilled by Fowler


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