Thursday, September 19, 2013

3 Styles: Iterative, Incremental and Evolutionary Agile (part 1)

When I’m teaching training courses (as I was this week at Skills Matter) or advising clients on the requirements side of software development (which I’m doing a lot of just now) I talk about model I call “3 Styles of Agile”. Incredibly I’ve never blogged about this - although the model is hidden inside a couple of articles over the years.

So now the day has come… I don’t claim the “3 Styles model” is the way it should be, I only claim it is the way I find the world.

While “doing agile” on the code side of software development always comes back to the same things (stand-up meetings, test/behaviour driven development, code review/pair programming, stories, boards, etc.) the requirements side is very very variable. The advice that is given is very variable and the degree to which that advice is compatible with corporate structures and working is very variable.

However I find three reoccurring styles in which the requirements side operates and interfaces to development. I call these styles: Iterative, Incremental and Evolutionary, and I usually draw this diagram:

I say style because I’m looking for a neutral word. I think you can use Scrum, XP and Kanban (or any other method) in any of the three styles. That said, I believe Kanban is a better fit for evolutionary while Scrum/XP are a better fit for Iterative and Incremental.

I try not to be judgemental, I know a lot of agile folk will see Evolutionary as superior, they may even consider Evolutionary to be the only True Agile but actually I don’t think that is always the case. There are times when the other styles are “right.”

Let me describe the three styles:


In this style the development team are doing lots of good stuff like: stand up meetings, planning meetings, short iterations or Kanban flow, test driven development, code review, refactoring, continuous integration and so on. I say they are doing it might be better to say “I hope they are doing” because quite often some bit or other is missing. Thats not important for this model. The key thing is the dev team are doing it!

In this model requirements are arrive in a requirements document on mass. In fact, the rest of the organization carries on as if nothing has changed, indeed this may be what the organization wants. In this model you hear people say things like “Agile is a delivery mechanism” and “Agile is for developers”.

The requirement document may even have been written by a consultant or analyst who is now gone. The document is “thrown over the fence” to another analyst or project manager who is expected to deliver everything (scope, features) within some fixed time frame for some budget. Delivery is most likely one “big bang” at the end of the project (when the team may be dissolved.)

In order to do this they use a bacon slicer. I’ve written about this before and called it Salami Agile. The requirements document exists and the job of the “Product Owner” is to slice off small pieces for the team to do every iteration.

The development team is insulated from the rest of the organization. There is probably still a change review board and any increase scope is seen as a problem.

I call this iterative because the team is iterating but thats about it. This is the natural style of large corporations, companies with annual budgets, senior managers who don’t understand IT and in particular banks.


This style is mostly the same as Iterative, it looks similar to start with. The team are still (hopefully) doing good stuff and iterating. There is still a big requirements document, the organization still expects it all delivered and it is still being salami sliced.

However in this model the team are delivering the software to customers. At a very lest they are demonstrating the software and listening to feedback. More likely they are deploying the software and (potential) users can start using it today.

As a result the customer/users give feedback about what they want in the software. Sometimes this is extra features and functionality (scope creep!) and sometimes it is about removing things that were requested (scope retreat!). The “project” is still done in the traditional sense of everything in the document is “done” but now some things are crossed out rather than ticked. Plus some additional stuff might be done over and above the requirements document.

I call this incremental because the customers/users/stakeholders are seeing the thing grow in increments - and hopefully early value is being delivered.

I actually believe this is the most common style of software development - whether that work is called agile, waterfall or anything else. However in some environments this is seen as wrong, wrong because the upfront requirements are “wrong” or because multiple deliveries need to be made, or because the team are’t delivering everything they were originally asked to deliver.


Here again the development team are iterating much as before. However this time there is no requirements document. Work has begun with just an idea. Ideally I would want to see a goal, an objective, an aim, which will guide work and help inform what should be done - and this goal should be stated in a single sentence, a paragraph at most. But sometimes even this is missing, for better or worse.

In this model the requirements guy and developers both start at the beginning. They brainstorm some ideas and select something to do. While Mr Requirements runs off talk to customers and stakeholders about what the problem is and what is needed the tech team (maybe just 1 person) get started on the best idea so far.

Sometime soon (2 weeks tops) they get back together. Mr Requirements talks about what he has found and the developers demonstrate what they have built. They talk some more and decide what to do next.

With that done the developers gets on with building and Mr Requirements gets on his bike again, he shows what has been built and talks to people - some people again and some new people. As soon as possible the team start to push software out to users and customers to use. This delivers value and provides feedback.

And so it goes. It finishes, if it finishes, when the goal is met to the organization decided to use its resources somewhere else.

Evolutionary style is most at home in Palo Alto, Mountain View and anywhere else that start-ups are the norm. Evolutionary is actually a lot more common than is recognised but it is called maintenance or “bug fixing” and seen as something that shouldn’t exist.

Having set out the three styles I’ll leave discussion of how to use the model and why you might use each style to another entry. If you want to know more about each model and how I see Agile as spectrum have a look my 2011 “The Agile Spectrum” from ACCU Overload or the recently revised (expanded but unfinished) version by the same title: “Agile Spectrum” (the 2013 version I suppose, online only).

1 comment:

  1. I smile at inference to "scope creep". Its only scope creep if un-managed. If managed, then time and cost are also reviewed as a consequence. "Scope creep" is where more (or less) is expected without corresponding agreement on compensating for time and cost.

    I'd also suggest that the risk of "scope creep" increases with Iterative to Incremental to Evolutionary.

    Evolutionary looks good for a small start-up. On the other hand, it could be costly for a internal development in a large organisation if there is insufficient discipline to match it at the Business and architecture levels of change as well.


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