Is there any use of the V-model?

This blog post originated with some thoughts when I attended the 13th International Conference on Agile Software Development in Malmö Sweden. As usual when I listen to presentations these tend to trigger new liner of thoughts instead of pondering the details of what was said. I guess this is a flaw in how I internalise knowledge from others.

Not surprising, nobody here mentioned the V-model since this is a conference e for those already embracing the gospel of agile development. Too bad, since I think the V-model is one of the most important metaphors regarding system (and software) development there is. But it is also on of the metaphors that have been used in ways which are completely inappropriate.

My “condensed understanding” of the strengths of the V-model is this: It defines a set of activities on the left side of the V with associated artefacts aimed at exploring the problem and detailing the solution down to the actual product (the code!). The important part is that these design activities have corresponding activities of verification & validation on the right hand side of the V, in a one-to-one relationship between the design and V&V activity. The number of levels is individual, but usually about 3-5, including code is reasonable.

Where it goes wrong is when the V is laid out in time as a template for progress of a project. This may make sense if you are designing for manufacturing-heavy products, but is useless for software, the time between understanding the problem (top-left part of the V) and where you verify that your implemented understanding is correct is just way too long to be competitive. There are also drawbacks since when project schedules are tight it tends to squeeze the V&V efforts on the right hand side of the V. This is definitely not news for software developers, and is a key point in agile software development (but probably phrased differently).

It seems to me that in order to optimise the efficiency and speed there is instead a tendency to downplay the activities above the point of the V ( the working code). Big-upfront-design is seen as such a bad thing that a projects ends up in with no design at all, there is a direct jump between formulating the problem (e.g. user stories) and start coding. I believe that in an agile project all activities in a V must be executed in each sprint in order to claim to be “truly agile”. Each sprint means a better understanding the problem, a better design to solve it, and a better implementation in the code. Of course all of these are also verified and validated to the required quality or acceptable level of risk. That does not say that these activates are equally large, or the size of the V is the same in alls sprints, but if you leave out the conscious architecture in the sprints you don’t learn to do better in the next sprints.

You should design the sprint activities in the V to provide the maximum added value with respect to the spent effort (which obviously depends on thousands of context-specific factors), but saying they are irrelevant is only reasonable for the simplest of systems, where you have a definition of the problem and code.

Personally I rather define the result of the activities, i.e.the artefacts, and let the teams decide themselves on how to populate them. I know blog readers may cry about excessive documentation, but what I am talking about is the necessity to externalise information necessary to share between developers, and teams, and to preserve this information over time, something which code never can do.

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