The Timeless Way of Building: Diagnosis and Repair

Architect Christopher Alexander's A Pattern Language is well known among programmers as the inspiration for the Design Patterns school of thought, but for some reason his other books are less widely read. My mother and father are both architects—"real" ones, not "software architects." :) My own amateur interest in the subject led me to read several of Alexander's books over the past couple of years.

The Timeless Way of Building is the first volume of an open-ended series. (A Pattern Language is the second.) It is in this book that Alexander first lays out the idea of a pattern language. More importantly, he explains an entire theory and practice of design and construction, of which the pattern language is only one piece.

Another piece of the Timeless Way is the practice of diagnosis and repair. Rather than a detailed plan of future projects, Alexander prefers to maintain a diagnosis of current problems. Each new project must be targeted at fixing these existing problem in the system: "At every moment we use the defects of the present state as the starting point for the definition of the new state" (p. 485). Alexander's goal is to create a type of spontaneous growth and order that is possible when change is incremental and decision-making authority is decentralized.

Alexander was hired to produce a new type of master plan for the University of Oregon campus. The result was published as the third volume in the "Timeless Way" series: The Oregon Experiment. In it, he writes again about diagnosis and repair:

It is still not clear where global order will come from, without a master plan.… How is the problem solved in an organism? Essentially, the problem is solved by a process of diagnosis and local repair.… The master plan tells us what is right for the future. The diagnosis tells us what is wrong for the present. (p. 146–148)

In software, the same problems and conclusions have led to "agile" processes, which emphasize incremental change and flexible planning. But I haven't seen any software companies adopt a consistent practice of "diagnosis"—keeping track of what's wrong or unsatisfactory with the current system. This extends beyond defect tracking; it should include a constantly updated list of code that, although it works, is hard to understand, difficult to change, or otherwise likely to cause problems. (This should be easy to generate—every programmer knows certain parts of their code base that they dread working on for one reason or another.) This knowledge can then guide new development to include "repair" and address such problems before they become defects. I've applied this on a small scale to my own work, and now I wish I had used it at Amazon, where my team spent much more time maintaining and improving old code than writing new code.