Principles for good requirements

The requirements specification is a document that contains all the constraints that any viable solution should satisfy. These can be categorised into requirements that

  • Must be satisfied (demand)
  • Should be satisfied (wish)

The wishes can also be prioritised to help evaluate solutions that satisfy different wishes.

A good requirements specification should be

  • Solution independent
  • Specific, objective, and quantified where possible
  • Measurable and testable
  • Traceable so that the source of the requirement is understood
  • Accurate in their representation of the true needs
  • Complete such that any solution that meets the requirements will be satisfactory
  • Well structured
Examples of requirements statements
Poor statements Better statements
"The product should be easy to use" "The product should be usable by 95% of adults aged 16-70"
"The maximum opening angle of the car door must be greater than 80 degrees" "The front seats must be accessible from a wheelchair"
The Toyota Porte has a large sliding door, enabling easier access.

The Toyota Porte uses a novel solution for enabling access to the car seats, which might have been overlooked if the specification prescribed a conventional hinged door