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.

Objective
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.

3a. Map these non-functional product requirements to the following categories: Simplicity, Performance, Features,  Economy (+ or - for complement or conflict). 

3b. (Online version) Use a Jamboard to draw the trade-off diagram (link). Each group draw numbered arrows with plus or minus indicators (+/-) to complete the diagram, illustrating the relationships between the requirements listed. 

Discussion:

• Do requirements influence design decisions?
• Is a unique solution possible satisfying all 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?

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

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A Collage of Outputs from the Requirements Exercise