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Non-functional requirement (NFR) is a requirement that specifies criteria that can be used to judge the operation of a system, rather than specific behaviors.
They are contrasted with functional requirements that define specific behavior or functions. 

Wikipedia: https://en.wikipedia.org/wiki/Non-functional_requirement

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Non-functional requirements are criteria to judge that the system performs its functions the right way. For instance, the max downloaded file size is 1 Gb, it should be downloaded within 12 seconds, etc.

Examples

• Scalability
  It tells what amount of data or number of users the system should be able to process.
  
  
• Performance
  How fast a certain system functions should be performed.
  
  
• Fault tolerance
  How fast the system should be restored in case of an unexpected issue.

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https://docs.google.com/spreadsheets/d/1x7_yoJNtx_S90iVowrJB64oJt87nsBFJIauyYp87MPc/edit?usp=sharing

Alternatively, existing NFRs spreadsheets could be added to the following directory:

https://drive.google.com/drive/folders/1RJZ3fCJBAZYQcbfudXZ0w6D-2MH17W2T

They could be added in as-is format, however, it is recommended to eventually convert them to the proposed format.

It will help to make sure all major NFRs are collected. Also, it is easier to work with spreadsheets if they all have a single format.

It is recommended to make sure:

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