system of systems (SoS)

What is a system of systems?

A system of systems (SoS) is the collection of multiple, independent systems in context as part of a larger, more complex system. A system is a group of interacting, interrelated and interdependent components that form a complex and unified whole.

These independent and possibly distributed systems pool their resources together, creating a new and more complex system. Individual systems in an SoS work together to provide functionalities and performance that none of the independent systems, or constituent systems, could accomplish on their own.

The goal of an SoS architecture is to get maximum value out of a large system by understanding how each of the smaller systems works, interfaces and is used. Such system designs require systems thinking -- a holistic approach to analysis that focuses on the way constituent parts interoperate, work over time and function within the context of a larger, evolving system.

The method for defining, abstracting, modeling and analyzing SoSes is called system of systems engineering. Many systems engineers (SEs) work within the context of an SoS. The constituent systems in an SoS may be developed by SEs independently and may continue to change over time independently.

In the data center, independent components of a large-scale system are connected through SoS-defined software interfaces called middleware. Such programs ensure that constituents do not compete for subtasks within the larger system and provide messaging services so that constituent systems can communicate. Constituent systems can also be geographically distributed.

Introduced in 2016, the International Organization for Standardization (ISO) adopted standards for SoS engineering. In 2019, the following three standards were adopted:

  • ISO/IEC/IEEE 21839 -- SoS considerations in lifecycle stages of a system
  • ISO/IEC/IEEE 21840 -- Guidelines for the utilization of ISO/IEC/IEEE 15288 in the context of SoS
  • ISO/IEC/IEEE 21841 -- Taxonomy of systems of systems

Why is a system of systems important?

A system of systems connects seemingly different systems with a larger, more complex configuration of systems. SoSes enable the creation and operation of large and complex systems, such as manufacturing supply chains or the numerous systems in an airplane, for example.

SoSes maintain operational independence of component systems, which also independently change over time as they are managed. Systems engineers create frameworks to improve SoSes. They help make decisions in evolutionary development, as well as determine infrastructure, policy or technology while also helping to solve any issues that appear. SoS issues are typically complicated and may require intense resource or monetary investments.

What are the types of system of systems?

There are four types of system of systems: directed, acknowledged, collaborative and virtual. In most cases, an SoS is a combination of these types and may change over time. The type of a SoS is based on the degree of independence of its constituents as noted below:

  • Directed. The SoS is created and managed to fulfill a specific purpose and the constituent systems operate independently. However, independent operation is treated as less important.
  • Acknowledged. The SoS has a specific purpose, but the constituent systems maintain independent ownership, objectives and development. Changes made in this SoS type are based on cooperative agreements between the system and the SoS.
  • Collaborative. Component systems freely interact with each other to fulfill a defined purpose. Management authorities have little impact over the behavior of the component systems.
  • Virtual. The SoS does not have central management authority or a centrally agreed-upon purpose. Typically, the acquisition of a virtual SoS is unplanned and is made up of component systems that may not have been designed to be integrated. Once its use is over, the components are normally disassembled and no longer operate in an SoS.

System of systems applications and examples

A system of systems can be applied in many settings. For example, they may appear in the following:

  • Business. SoS can be found in banking and finance systems.
  • Education. Universities such as Purdue, MIT and the Georgia Institute of Technology work on SoS problems.
  • Government agencies. The Department of Defense (DoD), the U.S. Federal Aviation Administration and NASA support research in systems of systems.
  • Healthcare. Systems can be found in personal health management services and regional facilities management.
  • Media. Systems can be found in film, radio and television.
  • Transportation. SoS can be found in air traffic management systems, national and international rail network systems, cargo transport, highway management, as well as space transportation systems.

An airplane, which is a large and complex system, is a specific example of a system of systems. Many different systems and devices all have to work together to operate different parts of the plane but can only work when all the essential systems work together.

Likewise, a manufacturing supply chain can only operate when all its integral systems operate together. This includes the integration of IT platforms, infrastructure and control structures.

Embedded automotive systems are another example of a system of systems, as they have numerous onboard computing, control and communication-based systems that all work together to improve safety, fuel efficiency and emissions. Safety systems could be considered their own SoS, with airbag deployment, collision impact warnings, seatbelt pretensioners, antilock and differential braking, as well as traction and stability control all working together to increase vehicle safety.

Learn more about system engineering skills and how they are needed for IT ops and serverless infrastructure.

This was last updated in June 2022

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