Gavin Terrill's Blog: Remembering Carl Adam Petri

Just found out that Carl Adam Petri passed away July 2, 2010. Petri invented the "Petri Net" - a tool for modeling process flow that is used in a wide variety of applications, from circuit design to traffic light coordination to business process management.

I was introduced to Petri Nets by a grizzled veteran software developer back when I knew everything. I looked into it and was struck by the simplicity of the model, plus the mathematics. You see, Petri Nets can be formally verified so you can prove that your flow is "correct", meaning it will complete and doesn't get stuck in an endless loop for example. You can even do simulations with it to help predict capacity requirements.

The basic idea is you have a diagram with boxes that represent "doing something", called a Transition. Transitions are connected to other transitions via a circle, called a Place. The connecting lines show the direction of the flow and are called Arcs. A network has start and end places and can not have cycles (i.e a Petri Net is a DAG).

Now, to model the process flow you place a Token in the starting place. The token represents a unit of work and moves through the network of transitions and places until it gets to the end place. As each transition fires the the token moves to one of the output places.

What is interesting is that a place can hold more than one token, so you can add another token to the starting place before the first one has reached the end place. This is why a Petri Net is good for modeling concurrent processes.

Wil Van Der Aalst has written some great papers on applying Petri Net theory to business process management. A few years ago I was inspired by one of his great books and created a Swing based Petri Net editor. The code has long since been lost unfortunately, but I remember feeling quite chuffed at being able to simulate and optimize an insurance claims process by playing with the capacity of certain transitions in order to improve overall system throughput. It was very Kanban like.

Petri was a true pioneer of our industry, and the amazing thing to me is that he came up with the idea when he was just 13!