When you visit the National Garden in the Imperial Palace grounds in Tokyo, they give you a plastic entrance card on entry. You return the card on exit at either the North or East gates of the palace. On first observation, it seems like a security scheme to insure that no visitor is not accidentally forgotten and remains in the grounds after 4.30pm. However, I wonder how well this scheme would work. Let's consider the variation in it.
On entry our guard couldn't decide if we were a party/family of 5 or 6. The 3 month old in the carrier around my neck ought to count but was it really necessary. As we shuffled through so did several other individuals and families. Had he really counted everyone accurately? On exit, it might have been easy to explain that the 3 month old didn't have a card whilst we secretly kept it as a souvenir (which we didn't, everyone in the party except me being a good upstanding Japanese citizen). I'm left wondering what the shrinkage of cards is each day? And how much search effort around the National Garden is required to be sure that the missing cards walked out the facility and aren't hiding in the bushes.
As a security system, I think the card system has more variability than would ideally be desired.
There is a second, simpler but less obvious reason for the cards - it's a Kanban system. The cards simply limit the inventory of people visiting the gardens to keep them from getting overcrowded. I strongly suspect this is the real reason. When the cards at the entrance run out, then new visitors need to wait until someone leaves. This is only likely to happen on very peak times such as New Year, the Emperor's Birthday and so forth. The Kanban solution has much lower susceptibility to variability. It doesn't matter if there is a small amount of shrinkage on an individual daily basis because it's a fail safe arrangement. So what if a few visitors have to wait a little longer to gain admission and the overall maximum inventory is reduced from shrinkage. The Kanban idea is much more variation tolerant.
I'm currently thinking a lot about Kanban systems and software engineering - after Don Reinertsen challenged me with it recently. He believes that the work I've been doing with cumulative flow diagrams will enable a Kanban system in tooling. The question is, what would be the benefit of such a system. It would certainly be easy to extend Visual Studio Team System to report inventory levels at different work item states and to limit the creation of new work items or movement of work items from state-to-state according to some Kanban limit. BUT, and this is the real question, for what purpose? I need to find a team willing to experiment with this idea manually and compare it against the drum-buffer-rope solution I have been evangelizing to see whether it is a flyer or not. Don't expect an answer to this question anytime soon.
