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 [1].” 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 [2]. 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 [3] ...  More

References
[1] A. Kosssiakoff, W.N. Sweet, S.J. Seymour, S.M. Biemer, Systems Engineering: Principles and Practices (Hoboken, NJ: John Wiley & Sons, 2011): 61.
[2] M.W. Maier, “Architecting Principles for Systems-of-Systems,” Systems Engineering, Vol. 1, No. 4, 1998, p. 271.
[3] A. Kosssiakoff, et. al., Systems Engineering, p. 62.