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I just realised that I’ve used the term ‘design hypothesis’ throughout this blog without a clear definition of what one is. 🙂

So here it is.

A design hypothesis is a prediction that a specific design will result in a specific outcome. A design hypothesis must:

  1. Identify the designs provenance, e.g the theory, practice or standards from it is derived.
  2. Provide a concise description of the design.
  3. State what the design must achieve in a verifiable fashion.
  4. Clearly identify critical assumptions that support the hypothesis.

Note that the concept of a fault hypothesis can be seen as a particular and constrained form of design hypothesis as, after Powell (1992), a fault hypothesis specifies assumptions about the types of faults, the rate at which components fail and how components may fail for fault tolerant computing purposes.

I give a short example of of a design hypothesis in the Titanic Part I post.


Powell, D., Failure mode assumptions and assumption coverage. In Proc. of the 22nd IEEE Annual International Symposium on Fault-Tolerant Computing (FTCS-22) , p386–395, Boston, USA, 1992.

The Titanic effect


So why did the Titanic sink? The reason highlights the role of implicit design assumptions in complex accidents and the interaction of design with operations of safety critical systems

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