Software Project Estimates: Go Fly a Kite!

Building Open Source software presents challenges to engineers and managers that differ greatly from proprietary systems. Open Source doesn’t eliminate the need for proper estimates and the predictability of costs that accurate estimates bring. Open Specifications like the W3C web standards add additional complexity to the estimation process. How are you supposed to know how long a project will take, when the specifications are frequently modified by authors and editors who aren’t under your control?

An estimation method that I often use at Mozilla is based on the Niagara Falls Suspension Bridge project. The Niagara Falls Suspension Bridge was the world’s first working railway suspension bridge. It was over 800 feet long, which was a length that was difficult to accurately measure back in 1847, before bridge construction started. The rapid waters and 225-foot high shear cliffs made a direct crossing impossible. The bridge construction must begin by stretching the first wire across the violent stream.

The Niagara Falls Bridge project shares many similarities with a complex software project: multiple stakeholders, unknown scope, dangerous obstacles and difficult terrain. How do you start when you can’t see how far you need to go? In January 1848, fifteen-year-old Homan Walsh flew a kite from the Canadian side of the river and was able to crash the kite into a tree on the New York side. The kite string was used to pull a thicker line back to Canada, then a rope, then metal wire, and construction progressed until a temporary suspension bridge could be built.

The truth is that Homan had a very difficult time getting the kite to fly to the other side! Weather and other unexpected problems left him stranded on the Canadian side for eight days and several failed attempts. Despite the difficulties, his initial kite was essential to the larger goal. When I first talk to engineers about a new software project, I often get estimates that sound like “two or three months, if we’re lucky.” When I hear that, I ask them to go fly a kite.

A “Kite” is just enough code to learn just enough new information about the project so that intelligent estimates can be made. I should note that this code can be very flimsy (like a kite) but functional enough to illuminate the unknown. It’s important that the engineer understands that we will not be shipping the kite! The goal with the kite exercise is to come with estimates that are in multiple pieces of work that each span days or weeks. Estimates that are still measured in weeks may require more kites to break down into days.

Getting that first kite across the gorge can be a very exhilarating experience, and may be just enough motivation to continue the difficult path forward. As an example, a big bridge project for us is Vertical Text and the first kite looked like this. A second kite looked like that.