Martin Robillard · Blog

Sustainable Software Design

10 February 2017 by Martin P. Robillard

There's a lot of interest in understanding software design as an activity. But what happens to the outcome of this activity? At one extreme, what happens on the whiteboard stays on the whiteboard (design is never explicitly captured). At the other extreme, design information is meticulously captured and archived, and then invalidated by the first decent refactoring. So without explicit effort, design knowledge just disappears. The consequence is that without design information developers will have to perform ignorant surgery. The temptation for ignorant surgery has to be related to the cost of maintaining accessible design information. When a particular design is expensive to describe and maintain, its description and rationale is at risk of being lost, no matter how awesome the underlying design ideas are.

So why don't we explicitly consider how expensive a particular design decision will be to capture and maintain consistent with the code, before adopting it?

There exist quality models for software design. They include attributes like reusability, flexibility, understandability. But, as far as I can tell we don't yet have an attribute that captures how cost-effective it is to describe a set of design decisions over time. That attribute is what I would call sustainability.

There's no techno-fix to make design more sustainable. It's a complex, multi-faceted problem. In this paper I review the areas of software development research and practice that relate to design sustainability and explain why they are not silver bullets. These include:

So, how to we move towards sustainable design? Maybe we can draw a lesson from gardening. At this point in our history we have the technology to grow anything anywhere. But the best way for a garden to stay alive with minimum effort is to select plants that are a good match for a specific environment. Likewise with design decisions. Different projects and systems have characteristics that are the equivalent of different types of soil, luminosity conditions, humidity. So we have to figure out how to select and nurture the design decisions that will thrive in these conditions.