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A primer on the design and science of complex systems

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Electrical networks, flocking birds, transportation hubs, weather patterns, commercial organisations, swarming robots... Increasingly, many of the systems that we want to engineer or understand are said to be ‘complex’. These systems are often considered to be intractable because of their unpredictability, non-linearity, interconnectivity, heterarchy and ‘emergence’. Such attributes are often framed as a problem, but can also be exploited to encourage systems to efficiently exhibit intelligent, robust, self-organising behaviours. But what does it mean to describe systems as complex? How do these complex systems differ from the more easily understood ‘modular’ systems that we are familiar with? What are the underlying similarities between different systems, whether modular or complex?

This primer introduces a domain-neutral framework and diagrammatic scheme for characterising the ways in which systems are modular or complex. The framework consists of basic system constructs and three fundamental attributes of modular system architecture: structural encapsulation, function-structure mapping and interfacing. These constructs and attributes are not tied to any formal modes of representation (e.g. networks, equations, formal modelling languages) nor to domain-specific terminology (e.g. ‘vertex’, ‘eigenvector’, ‘entropy’). Instead they provide an accessible domain-neutral language for describing complexity (e.g. in terms of emergence, self-organisation, heterarchy). This shared language allows researchers and practitioners from different disciplines to communicate their practices, solutions and methods, even when the systems they are working on appear superficially dissimilar.

The primer was produced by Dr Chih-Chun Chen and Dr Nathan Crilly in the EDC's Design Practice Group, funded by the UK's Engineering and Physical Sciences Research Council (EP/K008196/1).