Wednesday, 17 October 2018 07:02

Non-functional Requirements - Why do we need them?

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Non-functional requirements, what comes to our mind when we talk about NFR (Non-functional requirements)?

What do you put down in non-functional requirements when you are documenting requirements in your project?

When we say non-functional we typically mean those requirements that are not related to functionality of the system, then what exactly are these and why do we need them.

Now imagine a system where it publishes results for 10 graders school certification examination in a country like India, and the kind of load it will have when the results are declared.

So what all requirements do we have to consider for this system apart from functionality, it surely has to have high performance requirement to handle the load as well as good security/authentication system in place.

This is the kind of requirements which is generally referred as Non-functional requirements, the requirements which are important for the user community or for smooth functioning of the system like usability, reliability etc.

The non-functional requirements should always be described in clear terms like the system should be able to handle 0.1 million users simultaneously and the response time has to be less than 2 seconds for each user.


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Here is a good list of common non-functional requirements:

NFR Category

Non-functional Requirements

Short explanation

Applicable to situation

Can be tested by

Constraint

Price

Target price for the solution

Most

Checklist

Constraint

Resource constraints

Constraints imposed on development such as constraints imposed due to small screen size of mobile devices.

Most

Checklist

Compliance

Compliance

Regulatory compliance.

Health care (HIPAA, FDA)

Integration testing across systems

Compliance

Documentation

Documentation requirements.

Health care, Aviation, Automotive

Test cases for color blindness

Compliance

Legal and licensing issues or patent-infringement-avoidability

Adhering to compliance requirements.

Most

Test cases verification of record data update

Maintainability

Analyzability

Ability to investigate a failure

Most

Backup recovery test

Maintainability

Changeability

Ability to change one component without affecting others, and without causing unexpected failures

Most

Review the application code

Maintainability

Deployment

Ease with which an application can be deployed and upgraded.

Most

Review the application code

Maintainability

Escrow

Source code of an application is kept securely and available to buyer under certain conditions

Purchased an out-sourced product

Checklist

Maintainability

Extensibility / Modifiability

Ability to extend the product easily

Most

Consumer feedback

Maintainability

Supportability

Ability to support applications for specific period, locations etc.

Most

Checklist

Maintainability

Testability

Ease of test automation

Most

Checklist

Performance

Performance / response time (performance engineering)

Time taken to respond to a user request.

Most

Checklist

Performance

Resource utilization

% of available capacity used

Most

Checklist

Performance

Scalability

Ability to support specified number of users / transactions

Systems supporting large number of users

Review the application code

Portability

Interoperability

Ability to work with existing systems.

Most

Review the application code

Portability

Platform compatibility

Ability to work with stated platforms.

Most

Review the application code

Portability

Replaceability

 

Most

Review the application code

Reliability

Availability

% of time the system is available.

Critical systems

Latency testing

Reliability

Backup

Frequency at which data must be backed-up.

Universal

Test on desired platforms

Reliability

Disaster recovery

Time taken to restore the application after a disaster.

Most

Multiple browser test

Reliability

Failure management (Fault tolerance)

Ability to manage failures.

Most

Checklist

Reliability

Quality (e.g. faults discovered, faults delivered, fault removal efficacy)

Target defect density

Mission critical applications

Code and design Review

Reliability

Recovery / recoverability (e.g. mean time to recovery - MTTR)

Ability to recover quickly

Mission critical applications

Review the application code

Reliability

Reliability (e.g. mean time between failures - MTBF)

Ability to provide service when needed

Mission critical applications

Review the application code

Reliability

Replaceability

Ability to replace a faulty part on the fly

Mission critical applications

Review the application code

Reliability

Resilience

Ability to withstand attacks

Mission critical applications

Checklist

Reliability

Robustness

Ability to operate continuously even under adverse conditions.

Most

Simulation of internet attack
If hardware is present, heat cycle testing

Reliability

Stability

 

Most

Checklist

Security

Audit and control aka Accountability

To track changes made to data.

Finance, Health care

Review the application code

Security

Authenticity

 

Most

Review the application code

Security

Confidentiality

Protect data from being exposed to unauthorized users

Most

Review the application code

Security

Integrity

Maintaining correctness of data

Most

Penetration test

Security

Privacy

Ability to keep personal data secure.

Health care

Penetration test

Usability

Accessibility

Application being usable by persons with special needs such as color blindness.

Government

Review the application code

Usability

Ease of use

Limit number of clicks to maximum 3 clicks to complete any transaction

Most

Review the application code

Usability

Emotional factors (like fun or absorbing)

Making application likable by a certain audience.

Education

Checklist

Usability

Internationalization

Ability to operate the application in different countries such as handling multiple time zone, currency, languages etc.

Most

Review the application code

Usability

Learnability

Different user groups should be able to use the product with or without training

Most

Review the application code

Usability

Safety

Ensure safe usage of the product and prevent damages caused by the application. For example, safety features for a navigation system.

Where there are dangers to human life. Aviation, Automotive, Health care etc..

Key board control test

 

Certification

Certification on a particular technology such as certified on Azure.

Most

Untrained user test

 

Localization

Ability to satisfy needs of a particular country or domain (say petroleum industry)

Most

Review the application code

 

Re-usability

Ability to re-use existing components and create new re-usable components

Most

Review the application code

Portability

Installability

Ability to install or un-install easily

Most

Review the application code

Whereas some of the common functional requirements include:

  • Business Rules, logic, Validation
  • Calculations/formulae
  • Error message/handling
  • Transaction corrections, adjustments and cancellations
  • Admin functions/access, super user access
  • Authentication
  • Authorization levels
  • Audit log of transactions
  • External Interfaces
  • Reporting Requirements
  • Legal/Regulatory/Compliance Requirements

The non-functional requirements should always be described in clear terms like the system should be able to handle 0.1 million users simultaneously and the response time has to be less than 2 seconds for each user.

Advantages

  • Makes the system user friendly/easy to use and acceptable
  • Absence of them makes it lot more difficult to use for users and sometimes system may get abandoned due to the absence of these features

Disadvantages

  • Gets missed out often in requirements gathering exercise
  • Difficult to articulate or define quantitatively
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Ananya Pani

My mission is to help business analysts to build a successful professional career.

I have helped 2000+ BAs in choosing a better career and help them achieve professional success.

I co-founded Adaptive US, #1 IIBA V3 training organization. I manage sales and operations at Adaptive US. Under my leadership, Adaptive is now established as a world-leader.

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