What is Software Quality?

Software quality is an abstract concept. Its presence can be difficult to define, but its absence easy to see within moments. Thus, in the quest for improving software quality, it’s important to understand what it is.Wikipedia describes it as:

"In the context of software engineering, software quality measures how well software is designed (quality of design), and how well the software conforms to that design (quality of conformance). It is often described as the 'fitness for purpose' of a piece of software."

There are many other variations on the definition of software quality, but in broad terms, quality is referred to as the satisfaction of requirements. But what are requirements? Requirements can be categorized as functional and non-functional. Functional requirements refer to specific functions that software should be able to do. But we all know that just because a user can complete a task using the software, does not mean it has good quality. That’s because of the non-functional requirements not being met. For this purpose ISO developed ISO 25010 [1] as a model for specifying non-functional requirements. This model, shown below, illustrates the categorization of non-functional requirements.

Satisfying non-functional requirements such as performance and ease of use are typically done through inspection, meaning, going through the software, using it, and evaluating if the requirement is satisfied. So, as you can see, specifying the non-functional requirements and then satisfying them can be even more difficult than satisfying functional requirements. In summary, defining what software quality means to you and your software, and then developing a means to measure and evaluate it can help you improve. If you don’t know what you are measuring though, you can’t evaluate, much less improve!

[1.] ISO/IEC CD 25010 Software engineering -- Software product Quality Requirements and Evaluation (SQuaRE) -- Quality model and guide, 2009.

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