What are functional and non functional parts of an application?

I was asked this question in a开发者_如何学Cn interview.

What are functional and non functional parts of an application ?

Functional parts are those that relate to the function of the application - what it does.

Non functional are the parts that do not directly relate to the function - things like:

• performance
• quality
• portability
• maintainability
• quality
• availability
• extensibility
• and many more...

For example, in a calculator application, the functional parts are how the input and output work and the calculation logic/operation itself.

Non functional would be the usability, quality, performance and other aspects that do not have direct bearing on the calculator operations.

Functional relates to the features of the application. i.e. what it does. The non-functional parts are characteristics like:

• performance
• compatibility with previous versions
• security
• usability
• how well it performs under load
• how it handles failover scenarios