What are Complex Systems?
Complex Systems is a field of science studying how parts of a system give rise to the collective behaviours of the system, and how the system interacts with its environment. Social systems formed (in part) out of people, the brain formed out of neurons, molecules formed out of atoms, the weather formed out of air flows are all examples of complex systems. The field of complex systems cuts across all traditional disciplines of science, as well as engineering, management, and medicine. It focuses on certain questions about parts, wholes and relationships. These questions are relevant to all traditional fields. There are a range of characteristics that are common (but not necessarily always present) in complex systems. These are:
Why Complex Systems?
The study of complex systems is about understanding indirect effects. Problems that are difficult to solve are often hard to understand because the causes and effects are not obviously related. Pushing on a complex system "here" often has effects "over there" because the parts are interdependent. This has become more and more apparent in our efforts to solve societal problems or avoid ecological disasters caused by our own actions. The field of complex systems provides a number of sophisticated tools, some of them concepts that help us think about these systems, some of them analytical for studying these systems in greater depth, and some of them computer based for describing, modeling or simulating these systems.
Our Focus On Complex Systems:
What makes a project complex is not necessarily difficult. What makes a project complex can be a combination of a few key characteristics: scope ambiguity, multiple diverse stakeholders and non-linearity. Projects involving emergency recovery, large timelines with changing landscapes, experimental and uncertain innovations are all examples of projects that experience complexity and require additional tools and skills than a standard waterfall or agile approach.
Complex Adaptive Systems:
System where the individual elements act independently but jointly behave according to common constraints and goals. In the natural world, a flock of geese is a Complex Adaptive System (CAS). Human-intensive systems are also CASs since each human in the system is independent. (Complex Adaptive System (CAS) (glossary) - SEBoK)
Systems of Systems:
There are several definitions of system(s) of systems (SoS), some of which are dependent on the particularity of an application area. Maier (1998) postulated five key characteristics (not criteria) of SoS: operational independence of component systems, managerial independence of component systems, geographical distribution, emergent behavior, and evolutionary development processes, and identified operational independence and managerial independence as the two principal distinguishing characteristics for applying the term 'systems-of-systems.' A system that does not exhibit these two characteristics is not considered a system-of-systems regardless of the complexity or geographic distribution of its components.
In the Maier characterisation, emergence is noted as a common characteristic of SoS particularly in SoS composed of multiple large existing systems, based on the challenge (in time and resources) of subjecting all possible logical threads across the myriad functions, capabilities, and data of the systems in an SoS. As introduced in the article Emergence, there are risks associated with unexpected or unintended behavior resulting from combining systems that have individually complex behavior. These become serious in cases which safety, for example, is threatened through unintended interactions among the functions provided by multiple constituent systems in a SoS. ISO/IEC/IEEE 15288 Annex G (ISO, 2015) provides a definition of SoS:
System of Systems (SoS) — A system of systems (SoS) brings together a set of systems for a task that none of the systems can accomplish on its own. Each constituent system keeps its own management, goals, and resources while coordinating within the SoS and adapting to meet SoS goals. It should be noted that according to this definition, formation of a SoS is not necessarily a permanent phenomenon, but rather a matter of necessity for integrating and networking systems in a coordinated way for specific goals such as robustness, cost, efficiency, etc. (System of Systems (SoS) (glossary) - SEBoK)
Organisations can be treated as complex adaptive systems (CAS) as they exhibit fundamental CAS principles like self-organisation, complexity, emergence, interdependence, space of possibilities, co-evolution, chaos, and self-similarity. CAS are contrasted with ordered and chaotic systems by the relationship that exists between the system and the agents which act within it. In an ordered system the level of constraint means that all agent behaviour is limited to the rules of the system. In a chaotic system the agents are unconstrained and susceptible to statistical and other analysis. In a CAS, the system and the agents co-evolve; the system lightly constrains agent behaviour, but the agents modify the system by their interaction with it. This self-organising nature is an important characteristic of CAS; and its ability to learn to adapt, differentiate it from other self-organising systems. (Complexity theory and organisations)