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What is Non-Functional Requirement?

A Non-Functional Requirement (NFR) defines the quality attribute of a software system. They represent a set of standards used to judge the specific operation of a system. Example, how fast does the website load?

A non-functional requirement is essential to ensure the usability and effectiveness of the entire software system. Failing to meet non-functional requirements can result in systems that fail to satisfy user needs.

Non-functional Requirements allows you to impose constraints or restrictions on the design of the system across the various agile backlogs. Example, the site should load in 3 seconds when the number of simultaneous users are > 10000. Description of non-functional requirements is just as critical as a functional requirement.

In this tutorial, you will learn,

Types of Non-functional Requirement

  • Usability requirement
  • Serviceability requirement
  • Manageability requirement
  • Recoverability requirement
  • Security requirement
  • Data Integrity requirement
  • Capacity requirement
  • Availability requirement
  • Scalability requirement
  • Interoperability requirement
  • Reliability requirement
  • Maintainability requirement
  • Regulatory requirement
  • Environmental requirement

Examples of Non-functional requirements

Here, are some examples of non-functional requirement:

  1. Users must change the initially assigned login password immediately after the first successful login. Moreover, the initial should never be reused.
  2. Employees never allowed to update their salary information. Such attempt should be reported to the security administrator.
  3. Every unsuccessful attempt by a user to access an item of data shall be recorded on an audit trail.
  4. A website should be capable enough to handle 20 million users with affecting its performance
  5. The software should be portable. So moving from one OS to other OS does not create any problem.
  6. Privacy of information, the export of restricted technologies, intellectual property rights, etc. should be audited.

Functional vs Non Functional Requirements

Parameters Functional Requirement Non-Functional Requirement
What is it? Verb

Attributes

Requirement It is mandatory

It is non-mandatory
Capturing type It is captured in use case. It is captured as a quality attribute.
End-result Product feature

Product properties

Capturing Easy to capture

Hard to capture

Objective Helps you verify the functionality of the software. Helps you to verify the performance of the software.
Area of focus Focus on user requirement Concentrates on the user's expectation.
Documentation Describe what the product does Describes how the product works
Type of Testing Functional Testing like System, Integration, End to End, API testing, etc. Non-Functional Testing like Performance, Stress, Usability, Security testing, etc.
Test Execution Test Execution is done before non-functional testing. After the functional testing
Product Info Product Features

Product Properties

Advantages of Non-Functional Requirement

Benefits/pros of Non-functional testing are:

  • The nonfunctional requirements ensure the software system follow legal and compliance rules.
  • They ensure the reliability, availability, and performance of the software system
  • They ensure good user experience and ease of operating the software.
  • They help in formulating security policy of the software system.

Disadvantages of Non-functional requirement

Cons/drawbacks of Non-function requirement are:

  • None functional requirement may affect the various high-level software subsystem
  • They require special consideration during the software architecture/high-level design phase which increases costs.
  • Their implementation does not usually map to the specific software sub-system,
  • It is tough to modify non-functional once you pass the architecture phase.

Summary

  • A non-functional requirement defines the performance attribute of a software system.
  • Types of Non-functional requirement are Scalability Capacity, Availability, Reliability, Recoverability, Data Integrity, etc.
  • Example of Non Functional Requirement is Employees never allowed to update their salary information. Such attempt should be reported to the security administrator.
  • Functional Requirement is a verb while Non-Functional Requirement is an attribute
  • The advantage of Non-functional requirement is that it helps you to ensure good user experience and ease of operating the software
  • The biggest disadvantage of Non-functional requirement is that it may affect the various high-level software subsystems.

 

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