Complex engineered systems are large networks of technologies composed of many diverse subsystems, densely interacting in a nonlinear fashion to create a multi-tiered network system that evolves over time.1 To give some examples, we might cite airports, logistics networks, telecommunications networks, enterprise information systems, IoT platforms and the internet itself, hospitals and healthcare systems, the global air transportation network and all types of infrastructure systems from mass transit to water supplies. These more complex systems of technology differ from our traditional linear technologies in that they are open systems, composed of many autonomous components without any centralized locus of control or design.
Firstly, complex engineered systems are open systems, meaning that they have such a high level of interaction with their environment, that their boundary is not well defined. Added to this, they are composed of very many elements. We may be talking about millions, billions or even too many components for us to be able to quantify in any meaningful way. And it may be very difficult to say which of these components is part of the system and which are not. For example, metropolitan areas may span large geographical areas as different urban centers morph into each other. We might draw lines on a map in order to define jurisdiction, but from an engineering perspective they are largely arbitrary. Asking how many components there are in the system is again a somewhat arbitrary question. For all intents and purposes it is essentially infinite. We cannot itemize each component in the system. Added to this, components are leaving and joining, coupling and decoupling from the system in a dynamic fashion. Metropolitan areas provide critical services that a whole region or country’s infrastructure is dependent upon. They are deeply interconnected and interdependent on their environment. At this critical level of connectivity and interdependency, the system becomes more open than closed and it is defined less by its boundary and more by the flow of resources through the system.
As opposed to simple systems where components interact in a linear fashion, in complex systems components interact in a nonlinear pattern.2 Processes do not just take place from start to finish independently along one process. Instead, many different processes and functions are taking place within a parallel architecture. They interact across and between processes and domains in a network fashion. A metro area is a composite of many overlapping parallel infrastructure systems from transportation and water supply to the electrical power grid and the telecommunication networks. The components in the system are not just interacting across domains but also across scales. Complex engineered systems are what are called systems of systems. They have a multilayered hierarchical structure, as elements form part of subsystems, which form part of larger systems, which in turn form part of the whole system of systems. A subway train is part of the mass transit system, which is part of the transportation system, which in turn combines with many other systems to form the whole urban environment.
What is important within these composite systems of technology is how their different subsystems interrelate, that is, do they interact in a constructive or a destructive fashion. For example, is the airport in our metropolis built right beside a major residential area, resulting in noise pollution, a destructive relation that reduces the functionality of the whole system? Processes that were designed in isolation to function in a linear fashion lack integration with other systems in their environment. We get a dead-end effect and the production of waste that will be destructive to some other subsystems.
For example, when we build large tarmac surfaces that cannot absorb rainwater, the result is a high level of run off that needs to be dealt with by the wait water system. This is often the case when we use a reductionist design paradigm. It results in a focus on the individual components without full regard for how these components integrate to give us the functionality of the whole system. Thus, we often end up with optimal solutions on the micro level but sub-optimal solutions on the macro scale. When components interact in a constructive fashion, we get synergies. They complement and enable each other. We can think about the use of greenways and parks to absorb carbon emissions in a city, the coordination between consumers and producers of electricity on a smart grid, or the schedule coordination between different modes of transportation. These are examples of synergies.
Through synergies we get the emergence of new levels of organization and global functionality. Ultimately all of this technology and infrastructure that constitutes our an urban metro area is about delivering a material quality of life to citizens. Most of these infrastructure systems users don’t own. They just have access to the service. Material quality of life is not a single product or thing. It is about everything working together, so that we get the emergence of a seamless set of services enabling end users to live a high material quality of life. And these different types of relations and interactions are a defining factor in whether these infrastructure systems can deliver this emergent macro scale functionality that everybody wants. Synergies within complex engineered systems require both intelligent design and the use of information technology to coordinate different systems in real-time.
Complex engineered systems are really composite entities made up of many different elements and subsystems, heterogeneous components that were never really designed to work together. The system is distributed out, no one is really in control, and the whole thing is really just a network of connections. Our city is the product of thousands or even millions of different actors, businesses, deciding what project to invest in, public administrators deciding which project to support, citizens choosing where to live and send their children to school. All of these different actors and subsystems are only loosely associated with each other. Think about the Internet of Things where many billions of devices, from smartphones to tractors to hospitals couple and decouple from the system dynamically and operate under their own internal logic. These complex engineered systems are really networks that link up many heterogeneous subsystems and components.
Within complex engineered systems components are largely autonomous.3 They are not fully constrained by the system. This runs very much contrary to our traditional idea of engineering where control over the entire system is thought to be a prerequisite, with systems designed in a top-down fashion. But this is not how the Internet was created, nor electrical power grids, nor a metropolitan area. They all started small and evolved to become the complex systems they are today. Evolution is a process of development that acts on technologies on all scales. The electrical power grid is a good example, since its inception in the Industrial Age, electrical grids have evolved from local systems that serviced a particular geographic area to wider expansive networks that incorporate multiple areas typically covering a whole nation. At no point was there the option to simply build the whole national electrical infrastructure from scratch as a homogeneous system. The U.S. power transmission grid, for example, consists of about 300,000 km of lines operated by approximately 500 companies. And through distributed generation it is rapidly evolving into a next-generation smart grid that will expand the number of producers drastically, making for many, many, actors acting and reacting to each other’s behavior as the entire system evolves over time, which is an example of what is called complex adaptive systems.