Software Engineering is Not Computer Science

Contents

Engineering vs. Science

Beyond the Buzzword

Beyond the Buzzword

Some people think that "software engineering" is just a buzzword that means the same thing as "computer programming." Admittedly, "software engineering" has been misused. But a term can be abused and still have a legitimate meaning.

The dictionary definition of "engineering" is the application of scientific and mathematical principles toward practical ends. That is what most programmers try to do. We apply scientifically developed and mathematically defined algorithms, functional design methods, quality-assurance methods, and other practices to develop software products and services. As David Parnas points out, in other technical fields the engineering professions were invented and given legal standing so that customers could know who was qualified to build technical products. Software customers deserve no less.

Some people think that treating software development as engineering means we'll all have to use formal methods-writing programs as mathematical proofs. Both common sense and experience tell us that that is overkill for many projects. Others object that commercial software is too dependent on changing market conditions to permit careful, time-consuming engineering.

These objections are based upon a narrow and mistaken idea of engineering. Engineering is the application of scientific principles toward practical ends. If the engineering isn't practical, it's bad engineering. Trying to apply formal methods to all software projects is just as bad as trying to apply code-and-fix development to all projects.

Treating software as engineering makes clearer the idea that different development goals are appropriate for different projects. When a building is designed, the construction materials must suit the building's purpose. I can build a large equipment shed to store farming vehicles from thin, uninsulated sheet metal. I wouldn't build a house the same way. But even though the house is sturdier and warmer, we wouldn't refer to the shed as being inferior to the house in any way. The shed has been designed appropriately for its intended purpose. If it had been built in the same way as the house, we might even criticize it for being "over-engineered"-a judgment implying that the designers wasted resources building the shed and that the shed was therefore poorly engineered.

In the software field, a well-run project can be managed to meet one or more of the following product objectives:

Each software project team should define the relative importance of each characteristic explicitly, and then it should conduct the project in a way that achieves the project's objectives.

In most kinds of engineering, minimizing the cost of materials is an important objective. One way that software projects differ from engineering projects is that labor costs can account for almost 100 percent of the total project cost. In other kinds of engineering, the cost of materials can contribute 50 percent or more to the total project cost. Some engineering companies report that they automatically regard projects with labor constituting more than 50 percent of project cost as high risk. Most engineering projects focus on optimizing product goals; design costs are relatively insignificant compared to manufacturing and production costs. Because labor cost makes up such a large part of total software project costs, software projects need to focus more on optimizing project goals than other kinds of engineering do. So, in addition to working toward product objectives, a software team might also work to achieve any of the following project objectives:

Each software project must strike a balance among various project and product goals. We don't want to pay $5,000 for a word processor, nor do we want one that crashes every 15 minutes (though it hasn't been all that many years since we put up with both).

Which of these specific product and project characteristics a project team emphasizes does not determine whether a project is a true "software engineering" project. Some projects need to produce software with minimal defects and near-perfect reliability-software for medical equipment, avionics, anti-lock brakes, and so on. Most people would agree that these projects are an appropriate domain for full-up software engineering. Other projects need to deliver their software with adequate reliability but with low costs and short schedules. Are these properly the domain of software engineering? One informal definition of engineering is "doing for a dime what anyone can do for a dollar." Lots of software projects today are doing for a dollar what any good software engineer could do for a dime. Economical development is also the domain of software engineering.

Today's pervasive reliance on code-and-fix development-and the cost and schedule overruns that go with it-is not the result of a software engineering calculation but rather of too little education and training in software engineering practices.

The Right Questions

Software development as it's commonly practiced today doesn't look much like engineering, but it could. Once we stop asking the wrong question, "Is software development really engineering?" and start asking the right question, "Should professional software development be engineering?" we can start answering the really interesting questions. What is software engineering's core body of knowledge? How should professional software engineers be educated? Should professional software engineers be certified or licensed? Should software companies be licensed? Should the software itself be licensed? And, perhaps the most interesting question of all: what will the software industry look like after all these questions have been answered?

Steve McConnell is president and chief software engineer at Construx Software, where he divides his time between leading custom software projects, teaching classes, and writing books and articles. He is the author of the Microsoft Press books Code Complete (1993), Rapid Development (1996), and Software Project Survival Guide (1998). His books have twice won Software Development magazine's Jolt Excellence Award for outstanding software development book of the year. In 1998, readers of Software Development named Steve one of the three most influential people in the software industry along with Bill Gates and Linus Torvalds. In his spare time, Steve serves as editor in chief of IEEE Software magazine. He is on the panel of experts that provides advice to the Software Engineering Body of Knowledge (SWEBOK) project, and is a member of IEEE and ACM.

Steve earned a bachelor's degree from Whitman College and a master's degree in software engineering from Seattle University. He lives in Bellevue, Washington with his wife, Tammy; daughter, Haley; and dog, Daisy. If you have any comments or questions about this book, please contact Steve via e-mail at mailto:%20stevemcc@construx.com or via his web site at http://www.construx.com/stevemcc/

________________________________________________________

[Back to] Engineering vs. Science