Quality: What a Fuzzy Term


Most people in the software field don't seem to understand even the basics of what software quality means, even those who are labeled as quality "experts." They see it as being error free, satisfying users, meeting requirements, or hitting cost or schedule targets. But in reality, it's only partly about some of those things, and not at all about others. In this column, I try to set those erroneous viewpoints aright.

In this column (I pompously say) I am going to define the word "quality."

Don't quit reading now. I know quality, as an abstract topic, is boring. I know definitions are boring. But there's something strangely elusive about the topic of quality. In the novel Zen and the Art of Motorcycle Maintenance, for example, the pursuit of what quality means actually drove the main character crazy! And I think part of the problem is that we've been going about it all wrong. In other words, this is a contrarian column. If you like that kind of thing, read on!

First of all, I want to announce, here and now, that I think most people who write about quality don't know what they're writing about. Or more accurately, they actually do know what they're writing about, it's just not quality. Let me explain.

I frequently see explanations in software literature that equate quality to one of these:

  • a lack of errors
  • user satisfaction
  • meeting requirements
  • achieving cost and schedule targets

Let me dissect each one of these views. For the record, I think all of them are wrong!

First of all, quality is about far more than software errors, or the lack of them. My favorite definition of quality for the field of software-dating clear back to the early Barry Boehm thirty-something years ago-says that quality is a bunch of "ilities." It's reliability. It's usability. It's understandability. It's modifiability. It's testability. It's portability. It's a whole lot of stuff that sums up what it takes to be able to say a software product is of high quality (different people construct different lists of "ilities," but overall they agree much more than they disagree). Given that, how come quality isn't about just, say, errors? Because the error factor is what reliability is about, and that's just a small subset of the total topic of quality.

Now, how about all that other stuff, like user satisfaction and meeting requirements and hitting cost/schedule targets? Well, there is a relationship among all of those things, all right. But the beauty of that relationship is that it shows quality is distinct from all of them.

Here's that relationship: User Satisfaction = Compliant Product + Good Quality + Delivery Within Budget/Schedule.

What does it take to satisfy me as a user of (name a product!)? That the product meets my needs, that it has good quality (e.g., it doesn't fall apart as soon as I get it), and that I can get it when I need it for a cost I can afford. Is that the same as high quality?

For example, I can be satisfied with a McDonald's hamburger if it is what I expect it to be, has a little nutrition, and comes quickly and cheaply. I don't expect McDonald's to produce a high-quality meal, but I can be satisfied with what it does produce.

For a second example, I can be satisfied with a Jaguar automobile if it is as sleek and beautiful as I expect it to be, has plenty of power, is delivered when I want it, and I choose to pay the extremely high cost. But Jaguars, over the years, have not been known for high quality-they have balky electrical systems, for instance. But other aspects of the Jaguar's quality, such as fit and finish, are superb, and may make up for its shortcomings.

For a third example, I can be satisfied with the SAP mega-package information system if it does all the integrated enterprise transaction processing that I expect it to do, with a high degree of trustworthiness and

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