What are functional and non functional parts of an application ?

Question

I was asked this question in an interview.

What are functional and non functional parts of an application ?

Answer 1

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.

Answer 2

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