Last week I attended an Agile conference in Copenhagen. Among the speakers were David J. Anderson, who did a session on kanban systems. He told the audience the story of the kanban system used in the Imperial Palace in Tokyo, Japan. The Imperial Palace, is really like a big park with various buildings inside. I was in the park with my colleagues during our Japan 2008 Lean study tour last spring, and I remember being impressed with the kanban system used in the park, as a simple and truly elegant solution.

When you enter the park, which can be done at several different locations, you receive a little plastic brick. When you leave the park, you hand it back to the lady in uniform at the exit. My first thought was, that it was used to ensure that everyone got out before night. Interestingly that same answer came up at the conference when David Anderson asked the audience what they thought it was used for.

However, imagine a single plastic brick is missing when the park closes. Did someone loose their brick, or are they still inside the park? Should resources be spent on going through the park looking for them? With thousands of daily visitors, bricks will be lost probably on a daily basis, so it's not a way to ensure everyone gets out.

Instead it is a way to limit the number of concurrent visitors in the park. The number of bricks is limited to the highest number of concurrent visitors accepted. That means that the entrance booth may run out of bricks, and then stop letting more people into the park. They can start letting more people in when they get some of the bricks left at the exit. If a brick is lost? No big deal - that just lower the maximum number of concurrent visitors by one.

The concept is exactly what is also used in Lean manufacturing to control the amount of work-in-process. And of course it can also be used in software development environments to limit work to current capacity.

If you should ever go to Tokyo, I would highly recommend going to the park. It is quite beautiful.

By Sune Gynthersen