Contents  Introduction  The Basic Tenet  Ten Rules  Ten Rules (cont.)  Printable version

The basic tenet of ZDSD is this: Maintain your product in what you believe to be a defect-free state throughout the development process. This sounds simple, but it is a rare practice. The most common approach is to delay major testing until the final QA phase of software development, where defects are often discovered for the first time. Most bugs are not detected or fixed until long after their introduction. The longer a defect remains, the harder it is to fix. On large software products, each stage of development that a defect survives will increase the cost of fixing the defect by ten to fifty times. A defect introduced in the design phase can cost hundreds of times more to fix in the testing phase than it would if fixed immediately after its introduction.

By focusing on product quality throughout the development lifecycle, you will actually complete products faster than if you didn't pay attention to quality until the end of the project. The general rule of software quality is counter-intuitive: Improving quality actually reduces development time. This is because you eliminate all the time spent fixing bugs and reworking code, which can account for as much as 50% of development costs on a large project. The typical programmer writes between eight and twenty lines of code a day; the rest of the day is usually spent on debugging. ZDSD shortens schedules by eliminating most debugging time. Extensive studies done at NASA, IBM, and elsewhere have shown that better QA leads to shorter schedules. An IBM study concluded that software projects that make quality a top priority typically have the shortest schedules, the highest productivity, and even the best sales.

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