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Set Based Design

Each morning newspapers hit the newstands without fail. Live broadcasts are the same. Come show time they hit the air without fail. You can probably think of more examples of deadlines that are constantly achieved. So why does software development accept missed deadlines? Software development not only encourages software to be late, it has become accepted or just another risk to the project by default.


Implementing Lean Software Development introduces the concept of Set Based Design (SBD). SBD provides an answer on how to never miss a deadline every again, providing the deadline is feasible. SBD will allow software to constantly hit deadlines just as newspapers and TV shows do.

SBD requires multiple teams to implement the same functionality split over several sets (versions) of work. Each team works independently and in parallel to fulfil the same goal. This is in stark contrast to normal proceedings where each team is usually assigned to separate projects. At the end of the deadline the set that is best fit for purpose is chosen. This ensures the teams as a collective have delivered the best possible solution within the deadline. Each set should increase in scope and complexity. This means each additional set has a higher chance of missing the deadline.


The number of sets you decide upon is based on each variation, so there is no fixed limit. Assume three for the following introduction.

Set One
  • Start by accepting and acknowledging the deadline. This may be an integration deadline, a release or third party dependencies.
  • One of the teams should be working on the simplest thing that can possibly work. Some may say this is verging on a bodge or hack. You may end up adding logic to views, inserting business logic into sprocs or committing any other coding related atrocity. Despite this you must ensure the functionality is fit for purpose, tested and agreed by all.
  • The worst case scenario is the first set is released. You hit the deadline and you resolve some technical debt in the background afterwards.
Set Two
  • The team working on the second set would up their game. Still aiming for the deadline while the scope increases. Instead of adding logic into views, it goes into domain objects. Logic in sprocs? No chance. Other further enhacements could be added.
  • The worst case scenario? The deadline is missed but they have a solution which is better than the first set and close to completion.
  • After the first release the team simply finish up and deploy after the fact. This wipes out the technical debt of the first set and provides both a met deadline (via the first set) and the best possible solution.
Set Three
  • A third set would take a much higher level approach to the solution. This would be the best proposed solution. A strategic decision for the team factoring in long term goals and ambitions.
  • The chance of completing this set within the deadline are slim to none.
  • The worst case scenario is the team on the third set miss the deadline and one of the other two sets are released.
  • This is not the end of the world. Depending on how much work is left would dictate what happens. Scope could be further reduced, the set could be finished, or abandoned completely.


Is this waste?

No. The goal is to hit the deadline with the best possible solution. While a number of sets will never be released, the teams have hit their target. Teams should judge success on goal completion, not lines of code into production.

What are the downsides?

Trying to explain SBD and actually convincing the business to have a number of teams all working on the same project would sadly be an incredible challenge in most organisations.

When would you not use SBD?

SBD makes sense when there is a fixed scope deadline that cannot be missed. If this is not the case, iteration or refactoring at each step would suffice.


Producing an architecture that allows replacement or changes easily is another alternative, though this has risks of its own. Changeable architecture will be covered in a future post.


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