The Real FR vs NFR Requirements

Any professional working with requirements is familiar with the abbreviations FR (Functional Requirements) and NFR (Non-Functional Requirements). This categorisation attempts to distinguish one type of requirement from the other. It's an unfortunate exercise to separate them so distinctly because FRs often need to be described with their accompanying NFRs, while NFRs are often met by implementing a set of FRs.

However, we can reuse the FR vs NFR distinction in some other ways. Proposed below is a list of the more important ones:

Fictional vs Non-Fictional Requirements – Fictional requirements are not really requirements. They are designs, solutions, or wishes masquerading as requirements.  Non-fictional requirements are real requirements.

Factional vs Non-Factional Requirements – Factional requirements are those pushed for by only a certain set of stakeholders. Other stakeholders couldn’t care less about these. Non-factional requirements are required by the system and transcend individual factions.

Frictional vs Non-Frictional Requirements – Frictional requirements are contentious, either to some stakeholders or to other requirements. They also cause friction in the system development by causing the majority of the delays. 

Fallacious vs Non-Fallacious – Fallacious requirements are requirements that are properly written (they are Non-Fictional), but aren’t what is needed. Non-Fallacious requirements are requirements that are needed.

Fundamental vs Non-Fundamental – closely related are Fundamental requirements, which are essential to meeting the objectives. Non-Fundamental requirements are 'nice to haves'. Ironically, building only Non-Fundamental requirements does not result in a nice system.

Function vs Non-Function – Function requirements are about what the system needs the user to be able to do (‘The user must be able to cancel a transaction’). The user is replaced if they cannot perform the function. Non-function refers to user attributes and capabilities (‘The user must have the ability to view the most recent transactions' -- perhaps by possessing SQL skills?)

Familiar vs Non-Familiar – requirements that are common to many systems. These include management reports, etc. Non-familiar requirements are those that haven't appeared before in the project's collective experience.

Favourite vs Non-Favourite – Favourite requirements are flashy requirements sponsored by someone. They tend to be given attention. Non-Favourites languish or are implemented and tested perfunctorily. No one notices if they run away.

Falsifiable vs Non-Falsifiable – Falsifiable requirements are those that can be shown to not exist. Non-Falsifiable requirements cannot be proven to have been met. A quintessential example being ‘The system must be user friendly’. 

Fat vs Non-Fat – Fat requirements are a clump of requirements stated as one single requirement, often with multiple adjectives.  They tend to clog the process. Too many can result in a project heart attack. Non-Fat requirements are singular, and are processed through without harmful effect.

Fiscal vs Non-Fiscal – Fiscal requirements relate to cost ( ‘The solution shall not cost more than $X per transaction’)

Filial vs Non-Filial – Filial requirements are those that can be traced to a parent requirement. They show respect, and obedience, and conform to their parents wishes. Non-Filial requirements are either orphans or contradict their parent requirements. They cause family infighting and should be made to either conform, or else be cut off from family tree.

Fecund vs Non-Fecund Requirements - Fecund requirements are prone to keep popping out new requirements -- annoying, smelly, little new requirements that need lots of care and feeding.