Design, Develop, Create

Thursday, 11 June 2015

Exercise: Requirements Design Trade-off

This exercise has been adapted from Alexander’s ‘Notes on the Synthesis of Form’ (Alexander, 1964); the simple design problem from section 1 ‘the need for rationality.’ Alexander’s classic design tetrad characterises trade-offs between the major product requirements: simplicity, performance, features, economy.
Organise, model and explore the interrelationship between different requirements.
Requirements/Design Preparation
1. In groups of 2 or 3 categorise the following non-functional requirements for an imaginary high tech product.
Statement of non-functional requirements
  1. A simpler product (system, service, device) will be easier to manufacture and operate.
  2. A simple product with fewer features is going to be less costly to maintain.
  3. A simple product is easier to construct as it has fewer features.
  4. Greater system performance or power is achieved by including more (advanced) features.
  5. A highly optimised product is difficult to improve, change, fix or maintain without degrading its performance.
  6. A simpler product does not deliver as many features or options as a more complex product.
  7. A simple product using fewer specialised parts will not perform to as high a level as one using specialised optimised parts and sub-systems.
  8. Adding more features makes the product more difficult to maintain.

2. Consider following product requirements categories: Simplicity, Performance, Feature Set, Build/Operate Economy.

3. Each group to complete a diagram illustrating the trade-offs between the requirements list and the product requirement categories.


  • Do requirements influence design decisions?
  • Is there a unique solution that satisfies this statement of requirements?
  • Do requirements specify design?
  • Is it possible to overcome contradictory requirements?
  • Would more detail enable us to overcome contradiction?
  • Will computer modelling of requirements enable conflicts to be resolved?
  • Does the design of the product limit which requirements can be delivered?
  • Is there always a trade-off between requirements and design?

Alexander, C. (1964) Notes on the Synthesis of Form, Cambridge, Massachusetts, Harvard University Press.

A Collage of Outputs from the Requirements Exercise