Continuing my series of posts about Agile 2008, I will summarize the session presented by Rod Coffin and Don McGreal about Pull Systems.

We played a simple game to demonstrate the concept of a pull system. The goal of the system was to produce “Mr. Potato Paper Heads” of different variations: squared/triangle eyes with squared/triangle mouths (4 variations in total). The “production line” was divided in 4 phases:

  1. Cut the FACE
  2. Assemble the EYES
  3. Assemble the MOUTH
  4. Launch to MARKET

In a first round, we simulated a push system: the first person was responsible for cutting the face and drawing a specification of what should be built, by choosing the type of eyes and mouth. The next phases were responsible for cutting and glueing the eyes and mouth, respectively. The last phase would take the finished product and stick it to the wall, representing a launch to the market. We knew the market would consume 10 faces, but didn’t know how many of each type, so we had to guess.

At the end of the first round, the presenters showed what the market actually requested, counting revenues and wastes for each team. They then explained the concept of a pull system, that starts with the customer order and drives the upstream processes of the production line based on that.

In order to implement a pull system, we needed some buffers along the way (the mouth assembler would need at least one face of each different variation of eyes in order to build and deliver anything the customer ordered). As soon as an eye-only face was consumed, it triggered a signal to the eye-assembler to build another of that kind, to replace the buffer, creating another trigger to the upstream face-cutter (triggers are represented in red on the following picture, while green represents something being delivered).

Pull System

I think this was a very interesting and instructive session. It’s much easier to understand concepts in practice, by playing a game, instead of reading it in a book – or a blog ;-).

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