By Jim Grey (about)
I’ve said it to my test teams many times: Making software isn’t quite engineering. Building a bridge – now that’s engineering. You determine how long the bridge needs to be, how much load it needs to carry, and what kind of bridge to build (steel truss, concrete arch, etc.), and from there it’s mostly mathematics and physics. Just run the calculations and you’re good.
We have bridge-building down. With a couple of notable exceptions, such as the Tacoma Narrows bridge which heaved and twisted and finally collapsed (video here), new bridges seldom fail. Old bridges fail sometimes, but it’s reliably due to accident or neglect.
My apologies to any civil engineers who stumble upon this post. I’m sure you’re cringing that I’m overlooking many subtleties of your discipline.
There’s nothing subtle, however, about how often software fails. Our users aren’t happy about it, but they aren’t surprised by it, either.
For any thing you ask a software developer to build, there will be a whole bunch of valid ways to do it, each with its own unique ways of creating failures. This is especially true when when that developer enhances existing software that he or she didn’t make in the first place. It’s tough to predict exactly how the enhancements will affect the rest of the software. The more lines of legacy code, the more time and analysis it takes to think that through.
If a developer had unlimited time and money, it might be possible to deliver perfect software. Ah, a developer can dream! But here’s where bridge-building and making software have an important thing in common: time and money are never unlimited.
I sympathize with the folks who call software a craft. People who make software use tools and knowledge in its design and construction. These are hallmarks of craft.
Another way that software is like craft is that it’s difficult to fully separate the design from the making. Even when one person designs the software and another writes the code, the coder has to make a bunch of lower-level design decisions along the way.
The software craftsmanship movement meets corporate resistance because revenue and profit ride on what we build. Our companies need to sell features to meet revenue projections, or deliver bug fixes to retain customers. That’s why timed delivery is so important: if you wait too long to deliver, the opportunity to grow or retain revenue begins to shrink.
Feeling pressure to deliver, yet knowing that if we deliver junk we’ll be in an even worse pickle, we tend to manage software-development projects like engineering projects. I think we feel like we have better control when we manage them that way. But that feeling of control can’t mask it: no matter how tightly you plan a software project, no matter how you shape your development and delivery processes to mitigate risk, no matter how much you try to predict the troubles you’ll encounter, you will discover things along the way can seriously derail those plans. It happens in two-week scrum sprints just as it does in ten-month waterfall projects. Discovery is simply endemic to software development.
As a software project manager, I try to build in buffers for the unknown. I also steer projects daily based on what we discover, adjusting plans and communicating impacts to whomever needs to know. I try to make sure our development practices deliver the best possible code to test, and then I try to arrange testing to find the worst bugs first so that near the hoped-for end, only minor bugs remain. Despite all that, important bugs still sometimes reach the user.
We ship when the software is good enough. What “good enough” means varies from context to context, but it is unfailingly short of perfect. Shipping at good enough means you succeeded.
If I delivered bridges that way, I’d never drive over one I built.