3 Non-functional requirements

Define system properties and constraints e.g. reliability, response time and storage requirements. Constraints are I/O device capability, system representations, etc.

• Process requirements may also be specified mandating a particular CASE system, programming language or development method
• Non-functional requirements may be more critical than functional requirements. If these are not met, the system is useless

• Product requirements
  • Requirements which specify that the delivered product must behave in a particular way e.g. execution speed, reliability, etc.

• Organisational requirements
  • Requirements which are a consequence of organisational policies and procedures e.g. process standards used, implementation requirements, etc.

• External requirements
  • Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements, etc.

3.0.0.0 Non-functional requirement types  

• Product requirements
  • Usability reqts
  • Efficiency reqts
    • Performance reqts
    • Space reqts

  • Reliability reqts
  • Portability reqts

• Organisational requirements
  • Delivery reqts
  • Implementation reqts
  • Standard reqts

• External requirements
  • Interoperability reqts
  • Security reqts
  • Ethical reqts
  • Legislative reqts
    • Privacy reqts
    • Safety reqts

3.0.0.0 Non-functional requirements examples  

• Product requirement
  • 4.C.8 It shall be possible for all necessary communication between the APSE and the user to be expressed in the standard Ada character set.

• Organisational requirement
  • 9.3.2 The system development process and deliverable documents shall conform to the process and deliverables defined in XYZCo-SP-STAN- 95.

3.0.0.0 Non-functional requirements examples (cont.)  

• External requirement
  • 7.6.5 The system shall provide facilities that allow any user to check if personal data is maintained on the system. A procedure must be defined and supported in the software that will allow users to inspect personal data and to correct any errors in that data.