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, 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?

To address these questions, we produced a 'primer', which 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.

In addition to the primer and the related publications listed below, other related work includes a three-minute animated video introducing the subjective nature of complexity. These outputs were produced by Dr Chih-Chun Chen, Dr Eloise Taysom and Prof. Nathan Crilly, funded by the UK's Engineering and Physical Sciences Research Council (EP/K008196/1).

Related publications

Article presenting an empirically grounded framework for describing the complexity characterisations used by designers and scientists working on complex problems: Chen, C-C. and Crilly, N. Describing complex design practices with a cross-domain framework: learning from Synthetic Biology and Swarm Robotics. Research in Engineering Design, March, 2016.

Article examining the relationships between the concepts of system modularity, redundancy and degeneracy: Chen, C-C. and Crilly, N. Modularity, redundancy and degeneracy: cross-domain perspectives on key design principles. In 8th Annual IEEE International Systems Conference, Ottawa, Ontario, Canada, March 31-April 3 2014, IEEE 2014.

Article introducing a diagrammatic scheme for representing system resilience: Taysom, E. & Crilly, N. (2018) On the Resilience of Sociotechnical Systems, in P. Jones & K. Kijima (eds.) Systemic design: theory, methods, and practice (Translational Systems Science – Vol. 8). Berlin: Springer. pp. 145-171.

Article discussing the perspective-dependent nature of resilience: Taysom, E., & Crilly, N. (2017). Resilience in Sociotechnical Systems: The Perspectives of Multiple Stakeholders. She Ji: The Journal of Design, Economics, and Innovation, 3(3), 165–182.