System of Systems (SoS) (glossary)
(1) Two or more systems that are separately defined but operate together to perform a common goal. (Checkland 1999)
(2) an assemblage of components which individually may be regarded as systems, and which possess two additional properties:
(a) Operational Independence of the Components: If the system-of-systems is disassembled into its component systems the component systems must be able to usefully operate independently. That is, the components fulfill customer-operator purposes on their own.
(b) Managerial Independence of the Components: The component systems not only can operate independently, they do operate independently. The component systems are separately acquired and integrated but maintain a continuing operational existence independent of the system-of-systems. (Maier 1998, 267-284, pp. 267-284)
Source
Checkland, P. B. 1999. Systems Thinking, Systems Practice. Chichester, UK: John Wiley & Sons Ltd.
Maier, M. W. 1998. "Architecting principles for systems-of-systems." Systems Engineering, the Journal of the International Council on Systems Engineering (INCOSE) 1 (4): 267-84.
Discussion
There are many definitions of System(s) of Systems, some of which are dependent on the particularity of an application area. (Maier 1998) postulated five key characteristics of SoS: Operational independence of component systems, Managerial independence of component systems, Geographical distribution, Emergent behavior, and Evolutionary development processes. (Jamshidi 2009) has reviewed more than seven potential definitions of SoS and, although there is not all are universally accepted by the community, the following has received substantial attention:
A SoS is an integration of a finite number of constituent systems which are independent and operatable, and which are networked together for a period of time to achieve a certain higher goal.
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 them in a central way for specific goal such as robustness, cost, efficiency, etc.
DeLaurentis (DeLaurentis 2005) has added to the five SoS criteria above for SoS Engineering to include: inter-disciplinarity, heterogeneity of the systems involved, and networks of systems.
Not all SoS will exhibit all of the characteristics, but it is generally assumed that a SoS is characterised by exhibiting a majority of the Maier Criteria. Although the individual systems in a SoS are usually considered to have independent operational viability, it is sometimes the case that the SoS must contain some systems the only purpose of which is to enable the interoperation of the other component systems; i.e. the enabling systems cannot operate outside of the SoS.
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