What is software engineering?

I suppose if I’m going to have a tagline like “from programming to software engineering”, we ought to have some kind of shared understanding of what that journey entails. It would be particularly useful to agree on the destination.

The question “what is software engineering?” doesn’t have a single answer. Plenty of people have the job title “software engineer”, or work in the “engineering” department of a software company, so we could say that it’s whatever they do. But that’s not very constructive. It’s too broad: anyone who calls themselves a software engineer could be doing anything, and it would become software engineering. It’s also too narrow: the people with the job title “software engineer” are often the programmers, and there’s more to software engineering than programming. I wrote a whole book, APPropriate Behaviour, about the things programmers need to know beyond the programming; that only scratches the surface of what goes into software engineering.

Sometimes the definition of software engineering is a negative-space definition, telling us what it isn’t so that something else can fill that gap. In Software Craftsmanship: The New Imperative, Pete McBreen described that “the software engineering approach” to building software is something that doesn’t work for many organisations, because it isn’t necessary. He comes close to telling us what that approach is when he says that it’s what Watts Humphries is lamenting in Why Don’t They Practice What We Preach? But again, there are reasons not to like this definition. Firstly, it’s a No True Scotsman definition. Software engineering is whatever people who don’t do it properly, the way software craftsmen do it, do. Secondly it’s just not particularly fruitful: two decades after his book was published, most software organisations aren’t using the craftsmanship model. Why don’t they practice what he preaches?

I want to use a values-oriented definition of software engineering: software engineering is not what you do, it’s why you do what you do, and how you go about doing it. No particular practice is or isn’t software engineering, but the way you evaluate those practices and whether or not to adopt them can adopt an engineering perspective. Similarly, this isn’t methodology consultancy: the problems your team has with Agile aren’t because you aren’t Agiling hard enough and need to hire more Agile trainers. But the ways in which you reflect on and adapt your processes can be informed by engineering.

I like Shari Lawrence Pfleeger’s definition, in her book Software Engineering: The Production of Quality Software:

There may be many ways to perform a particular task on a particular system, but some are better than others. One way may be more efficient, more precise, easier to modify, easier to use, or easier to understand. Consequently, Software Engineering is about designing and developing high-quality software.

There’s a bit of shorthand, or some missing steps here, that we could fill in. We understand that of the many ways to build a software system, we can call some of them “better”. We declare some attributes that contribute to this “betterness”: efficiency, precision, ease of adaptation, ease of use, ease of comprehension. This suggests that we know what the properties of the software are, which ones are relevant, and what values a desirable system would have for those properties. We understand what would be seen as a high-quality product, and we choose to build the software to optimise for that view of quality.

The Software Engineering degree course I teach on offers a similar definition:

Software Engineering is the application of scientific and engineering principles to the development of software systems—principles of design, analysis, and management—with the aim of:

  • developing software that meets its requirements, even when these requirements change;
  • completing the development on time, and within budget;
  • producing something of lasting value—easy to maintain, re-use, and re-deploy.

So again we have this idea that there are desirable qualities (the requirements, the lasting value, ease of maintenance, re-use, and re-deployment; and also the project-level qualities of understanding and controlling the schedule and the cost), and the idea that we are going to take a principled approach to understanding how our work supports these properties.

Let me summarise: software engineering is understanding the desired qualities of the software we build, and taking a systematic approach to our work that maximises those qualities.

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About Graham

I make it faster and easier for you to create high-quality code.
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