Having a hard time thinking of nonfunctional requirements? Here are some categories and "trigger questions" that may help.

Trigger Questions

• User Interface nad Human Factors
  • What type of user will be using the system?
  • Will more than one type of user be using the system?
  • What sort of training will be required for each type of user?
  • Is it particularly important that the system be easy to learn?
  • Is it particularly important that users be protected from making errors?
  • What sort of input/output devices for the human interface are available and what are their characteristics?

• Documentation
  • What kind of documentation is required?
  • What audience is to be addressed by each document?

• Hardware Considerations
  • What hardware is the proposed system to be used on?
  • What are the characteristics of the target hardware, including memory size and auxiliary storage space?

• Performance Characteristics
  • Are there any speed, throughput, or response time constraints on the system?
  • Are there size or capacity constraints on the data to be processed by the system?

• Error Handling and Extreme Conditions
  • How should the system respond to input errors?
  • How should the system respond to extreme conditions?

• System Interfacing
  • Is input coming from systems outside the proposed system?
  • Is output going to systems outside the proposed system?
  • Are there restrictions on the format or medium that must be used for input or output?

• Quality Issues
  • What are the requirements for reliability?
  • Must the system trap faults?
  • Is there a maximum acceptable time for restarting the system after a failure?
  • What is the acceptable system downtime per 24-hour period?
  • Is it important that the system be portable (able to move to different hardware or operating system environments)?

• System Modifications
  • What parts of the system are likely candidates for later modification?
  • What sorts of modifications are expected?

• Physical Environment
  • Where will the target equipment operate?
  • Will the target equipment be in one or several locations?
  • Will the environmental conditions in any way be out of the ordinary (for example, unusual temperatures, vibration, magnetic fields)?

• Security Issues
  • Must access to any data or the system itself be controlled?
  • Is physical security an issue?

• Resources and Management Issues
  • How often will the system be backed up?
  • Who will be responsible for the back up?
  • Who is responsible for system installation?
  • Who will be responsible for system maintenance?