Follow on: Revisiting the Definition of Software Quality

Interesting article and discussion on the definition of quality on StickyMinds.com! Article is dated back to 2001, but it is still very much relevent. Robert L. Glass has done a good job in defining what quality is and what it is not. As you can read through the comments, not everyone agree with his definition - as one would expect. Quality is a FAT word and can be interpreted in zillion of ways. It is therefore important that the project team agrees to one definition of quality and stick to it. Consistency is far more important than the definition itself.

ISO definition of Quality: The totality of features and characteristics of a product or service that bear on its ability to satisfy stated or implied needs. (ISO 8402: 1986, 3.1)

This definition captures both funcional and non-functional requirements. And BTW, the official name of all "illities" is Systemic Qualities. And there are a lot more Systemic qualities than what Robert has mentioned - for instance - interoperabiliy, availability, scalability, etc.

Another point I disagree with Robert is that "customers/users must participate" in prioritizing and selecting "illities". Some of these systemic qualities are customer facing and other are company facing. For example, it is in companies best interest to make sure there is flexibilty in the code for future expansion and understandability is important to the company for maintenance purpose! Customer doesn't care if your code is moduler and your architecture is flexible. All he cares is the feature set he wants, when he wants it. Customer cares less about the business requirements. But when we talk about quality, all requirements come into picture:

• customer requiremens
  
• business requirements (capture market requirements and corporate requirements)
  
• legal requirements
• government requirements
• social requirements
• testability requirements
• operations requirements
• engineering requirements
  

I don't think we need to be in accordance with the customer on all these requirements!!

Another interesting topic that was raised in the article is whether quality can be quantified, given the definition by Robert Glass. I find it rather amusing because, I think, Quality can be defined and can even by quantified. Of cosurse, not everyone would agree with your definition and your way of quantifying it, but you can definetely do it. And as I said, consistency is far more important than the definition itself.

Read Quality Index (QI): Measure of Risk for more insight into how you can measure software quality