Short answer

There is no general rule - as the minimal amount depends on the system, its stakeholders, criticality, complexity, size and/or risks.

Longer answer

We suggest to always explain, document or specify the following aspects:

  • 3-5 central quality requirements, expressed in scenarios.
  • Context view and external interfaces
  • Brief explanation of your solution strategy, the most important decisions influencing the implementation or operation of the system.
  • Building block view, level 1.
  • Most important crosscutting concepts.