The theme of this book is that biological concepts are more useful than the physics toolbox when examining cyber risk. John Foster, in a paper published in the Cambridge Journal of Economics in 2005 (Vol 29, 873–892), developed a scheme for describing orders of complexity which has four levels.
In the hierarchy he sets out, physics and biology are just the first two steps in a sequence which then extends into psychology and economics. We will be using concepts from those two disciplines later (see views 17, 23, and 24) but for now here are the four levels of complexity described in his paper:
First order complex systems:
These are systems with purely physical components. A tornado, for example, is a complex structure that requires sophisticated non-linear mathematics to model its flow.