There are a number of quality requirements (also known as non-functional requirements) that have been explored over the years both in theory and practice. Examples are: performance, security, reliability.

Over the last decade, the field of software development has increasingly paid attention to User Experience (UX), as an emerging software quality that can act as one competitive edge for the software products and services. Still, many software development organizations face challenges in finding a suitable way to approach UX, and keep that on the agenda together with other quality requirements.

In my view, understanding similarities and differences between UX and more explored quality requirements can be one first step in addressing the challenges.

My question is:

What are the similarities and differences between UX (as a software quality) and more explored quality requirements (such as security, performance, reliability, etc.)?

I appreciate if you include concrete examples in your 'answers' when you compare the latter two categories.

2 Answers 2


I think UX is often miss-interpreted as design. Design is often an acquainted taste and therefor it is pretty much untestable, but usability testing is something different. It is important that user can use the product with only minimal training, but more important it should feel logical and non repetitive within the users mental model.

During evaluation of a new products, I spend less time thinking about possible security and or performance issues, then if it delivers what I expect from it. If the user experience is bad, I do how ever question if the product will also lack in the other departments. I think that UX therefor also functions as a form of marketing of the products reliability, although it might be irrelevant, it might set the tone of my thought process.

Just like security and or performance testing, usability testing is often not performed at all unless a client asks for it or when issues have arisen in the field recently. Its relatively expensive and the return on investment feels very low. The sales team can't sell a product without the needed features. They can sell stuff that is insecure, slow and which has a horrible user experience.

The user experience is the one thing that is most in your face and will make users happy far more then security and performance, unless your a bank. Since users do not care about security. Performance is only relevant if they know better and faster systems, but if its the only tool for the job often they will probably accept slowness as well. But extra clicks, ohboy! A chance of getting RSI, help! This is a real issue for most user groups. :)

A good read is Rocket Surgery Made Easy: The Do-It-Yourself Guide to Finding and Fixing Usability Problems, it suggests a solid strategy to find usability issues with only a fair amount of effort.

I am not really sure you can compare security, performance, reliability and usability testing. They all cover a different aspects of the software product lifecycle. Also the people who are concerned about these "requirements" topics have different roles and responsibilities within most companies.

  • Security: System administrators and public relations (due to privacy issues)
  • Performance: System admins, users and managers
  • Reliability: Legal department
  • Usability: Users and (efficiency) managers

I would wonder how can we estimate the risk of each group and where should we focus our efforts on. Development teams are always under time pressure, making their main similarity a question of can we afford to skip this type of testing or can we not.


more explored quality requirements

I don't know that I'd consider User Experience to be less explored than security or performance or any other category of software quality; maybe just newer. I'm no expert and I've only read a few books on the subject but I see more and more resources coming available on the topic. As for it being a requirement with equal footing to other quality categories, I think that's very dependent on the project environment.

what are the similarities and differences between UX (as a software quality) and more explored quality requirements (such as security, performance, reliability, etc.)?

If we look at a model like the Quality Criteria categories of the HTSM, we can see Usability (or how easy is it for a real user to use the product?) as one of the ten categories of quality we might consider important for a given project or product.

  • In fact if you've never viewed the Quality Criteria categories, I'd suggest you start there. You can probably generate a list of similarities and differences between many of them.

My impression:

UX seems like a far more salient subject for software developers to understand, especially when compared to something more nebulous like security.

  • For example, depending on the application, security can be a very important dimension of quality (think protecting user passwords, credit card numbers, etc.) but building and testing for security is a very difficult thing. How many different ways can some hacker or tester get access to a user's password?
  • UX by it's vary nature is more visual and more noticeable. As a consequence I think it's also easier to test for (or at least gives the impression of being easier to test for).

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