What is a System-of-Systems (SoS)?
A SoS results when independently useful systems are combined to achieve more functionality than just the sum of the systems before being combined. It is important to realize that just because a system is complex does not mean that it is a SoS. A SoS is an arrangement of “independent and useful systems [that] are integrated into a larger system that delivers unique capabilities .” This is a good explanation. Consider also the description of SoS developed by Mark W. Maier which emphasized operational independence of the components and the managerial independence of the components . By operational independence, Maier means that if the system is broken into its system parts, then each system must be able to continue to operate for customer oriented purposes. By managerial independence, the individual systems must not only have the capacity to operate independently, but they do actually operate independently. There are other criteria that can be used such as Geographical Distribution, Emergent Behavior, Evolutionary Development, Self-Organization, and Adaption .
What is an Example of a SoS?
An example of a SoS is the Ballistic Missile Defense System (BMDS). This is recognized as a SoS . This is because the behavior of the overall system is not explicitly apparent from the individual constituents. The BMDS system provides a capability that emerges from the combination of multiple, independently developed systems that are operated by various DoD services of the US government and allies.
How Does SoS Include Other Issues?
The result of systems engineering effort is an Engineered System. In fact, as Benjamin S. Blanchard and Wolter J. Fabrycky observe, “Systems can be engineered well or poorly … A well-engineered system has … [certain] characteristic .” A well-engineered system has concerned with “developing fundamental theories and methods to address the challenges of large-scale complex systems in context of their socio-technical environments .” In other words, Engineering Systems circumscribes a large footprint that includes social and technical issues.
What Are Some Examples Of SoS That Can Benefit From Systems Engineering?
An example of a SoS that can benefit from engineering systems is the transportation system. It consists of multiple independent systems that work together such as car, trains, roads, airplanes, and many other systems. Taken as a SoS, these elements can be better designed if other concerns are taken into account such as social and environmental. If systems engineering is applied to this SoS, then a larger community of users can benefit. As an example, the needs of economically challenged individuals can be met in a more efficient way if the train systems, bus systems, and road systems are engineering as SoS to improve access and synchronization with user schedules. Another example is that the environmental impact of fossil fuels can be optimized (minimized) if the engineering systems approach is taken by deploying the systems efficiently. In these ways, and many others, it is possible to apply systems engineering in a way that results in an engineered system that will have wide acceptance over a larger community of users.
 A. Kosssiakoff, W.N. Sweet, S.J. Seymour, S.M. Biemer, Systems Engineering: Principles and Practices (Hoboken, NJ: John Wiley & Sons, 2011): 61.
 M.W. Maier, “Architecting Principles for Systems-of-Systems,” Systems Engineering, Vol. 1, No. 4, 1998, p. 271.
 See, for instance, the list developed by A. Kosssiakoff, et. al., Systems Engineering, p. 62. Their list includes Geographical Distribution, Emergent Behavior, Evolutionary Development, Self-Organization, and Adaption.
 N. Davendralingam, D. A. Delaurentis, “A Robust Portfolio Optimization Approach to System of System Architectures,” Systems Engineering, Vol. 18, No. 3, 2015, p. 269.
 Benjamin S. Blanchard and Wolter J. Fabrycky, Systems Engineering and Analysis, 5th Edition (Upper Saddle River, NJ: Prentice Hall, 2011): 24.
 D.H. Rhodes, A. M. Ross, D.J. Nightingale, “Architecting the System of Systems Enterprise: Enabling Constructs and Methods from the Field of Engineering Systems,” IEEE SysCon 2009, Vancouver, Canada, March 23-26, pp. 190-195.