Systems of Systems

Definition: A system of systems (SoS) is "a collection of systems, each capable of independent operation, that interoperate together to achieve additional desired capabilities."

Keywords: system of systems (SoS)

MITRE SE Roles and Expectations: MITRE systems engineers (SEs) are expected to understand the characteristics of systems of systems and their implications for systems engineering in an SoS environment. This includes both considering the broader SoS context when engineering a system or service and applying systems engineering to the SoS as a system in its own right.

At MITRE, when we take an enterprise perspective, we recognize the larger SoS and the need to apply systems engineering at this higher level. In some cases, we see this need before our sponsors, whose organizations may be aligned with the individual systems with no mechanisms to address the larger SoS from a cross-cutting integrative perspective. In these cases, we face the challenge of finding ways to help our sponsors recognize the need for systems engineering across systems to address their enterprise needs.


In today’s networked world, very few systems, if any, stand alone. This is clearly the case with information technology (IT) systems and applications, as it is with most military, air traffic control, and other cyber-physical systems. In fact, some will argue that SEs need to realize that when they are developing systems, they are developing components or modules of larger systems, or "systems of systems."

Why is this important to systems engineering at MITRE? First, the systems most of MITRE’s sponsors develop or manage fit the preceding description of an SoS. Second, systems of systems have a set of characteristics that make direct application of systems engineering methods, tools, and techniques difficult, if not inappropriate. Therefore, it is important for SEs to understand what constitutes an SoS, which constituent systems they touch, and most important, how the context affects which systems engineering methods, tools, and techniques they apply.


Typically, the constituent systems (the systems that make up an SoS) are in service before the SoS is either created or recognized. The fact that the constituent systems are often developed independently and may continue to evolve independently adds to the complexity of the SoS. Furthermore, this independence of constituent systems brings with it a host of other practical considerations associated with management and governance because the authority relationships between the constituents and the SoS can overlap considerably.

Historically, SoS considerations are addressed from the bottom up, by developing systems that can interoperate with other systems, or less preferred, by addressing problems with interoperability once the systems are fielded. The preponderance of systems of systems makes it very important for SEs to pay particular attention to the larger context in which a system will be deployed when developing or updating systems to ensure that they effectively meet the larger needs of their users. The importance of addressing SoS considerations when developing or upgrading systems is discussed in the SEG's Engineering Systems in the Context of Systems of Systems article.

Increasingly, however, SEs are called on to treat the larger SoS as a system in its own right, as in air traffic management. Focusing only on the parts of the air traffic management system, without taking a broader view of the whole system, does not account for broader intricacies and interactions, and for unexpected emergent consequences. The same applies across defense systems supporting mission capabilities such as air and missile defense, anti-access area denial, force protection, global strike, satellite communications, and many other military applications. In these cases, MITRE sponsors are turning to us to bring effective systems engineering to these larger systems of systems. It is important for us to recognize when we are addressing a larger SoS and to apply effective systems engineering approaches in that context. This topic is addressed in the SEG's Treating Systems of Systems as Systems article.

Engineering across systems of systems to achieve a broader capability can be challenging, especially given the independence of the constituent systems and the fact that these constituent systems are on their own schedules for development and evolution. Taking a disciplined approach to addressing this complex engineering environment has been addressed in models that lay out a process to conduct analysis and coordinate changes over time. This topic is addressed in the SEG's Systems Engineering Life-Cycle Processes as Applied to Systems of Systems article.


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