29 lines
2.0 KiB
Markdown
29 lines
2.0 KiB
Markdown
---
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title: Nonfunctional Requirements
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---
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## Nonfunctional Requirements
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A 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 (a functional requirement). Non-functional requirements are often called "quality attributes", "constraints" or "non-behavioral requirements".
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In plain English, non-functional requirements are things that 100% is needed for the code to run. For example, a requirement would be to be able to login, but whether it takes 1 second to log in or 1 hour to login, both satisfy the functional requirement. The non-functional requirement would then be that the login time should take no more than 3 seconds.
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Informally, these are sometimes called the "ilities", from attributes like stability and portability. NFRs can be divided into two main categories:
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* **Execution qualities**, such as safety, security and usability, which are observable during operation (at run time).
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* **Evolution qualities**, such as testability, maintainability, extensibility and scalability, which are embodied in the static structure of the system
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Usually you can refine a non-functional requirement into a set of functional requirements as a way of detailing and allowing (partial) testing and validation.
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### Examples:
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* The printer should print 5 seconds after the button is pressed
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* The code should be written in Java
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* The UI should be easily navigable
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#### More Information:
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<!-- Please add any articles you think might be helpful to read before writing the article -->
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* [Wikipedia article](https://en.wikipedia.org/wiki/Non-functional_requirement)
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* [ReQtest](http://reqtest.com/requirements-blog/functional-vs-non-functional-requirements/) Explains the difference between functional and nonfunctional requirements
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* [Scaled Agile](http://www.scaledagileframework.com/nonfunctional-requirements/) Works through the process from finding to testing nonfunctional requirements
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