AS NZS ISO IEC IEEE 21839:2021 pdf download – Systems and software engineering – System of systems (SoS) considerations in life cycle stages of a system
4.1 System of systems
Both individual systems and SoS conform to the accepted definition of a system in that each consists of parts, relationships and a whole that is greater than the sum of the parts; however, although an SoS is a system, not all systems are SoS. Maier (1998) postulated five key characteristics (not criteria) of SoS: operational independence of component systems, managerial independence of component systems, geographical distribution, emergent behavior and evolutionary development processes. Maier identified operational independence and managerial independence as the two principal distinguishing characteristics for applying the term “systems-of-systems”. A system that does not exhibit these two characteristics is not considered a system-of-systems regardless of the complexity or geographic distribution of its components[5]. An essential characteristic is that each constituent system within the SoS is operationally independent. That is, each constituent system can operate independently to fulfil some number of purposes on its own. In an SoS, systems are also managerially independent. That is, each constituent system is likely to be managed by organizations with a level of independence, with potentially different goals and objectives for the constituent systems. In some cases, there may be a designated entity with some type of responsibility that spans an SoS. These managerial arrangements may be loosely defined or more highly structured depending on the particular situation. In other cases, no such entity may exist.
4.2 Constituent systems
An essential concept is that the system of systems is comprised of constituent systems (and may include other elements) that interact to provide capabilities that no one system or element in the SoS can provide by itself. Each constituent system is an independent system that provides capabilities to meet its specified mission or business objective and has its own life cycle, management and governance and technical requirements. Constituent systems include systems which are often considered as infrastructure, such as communications systems. A constituent system can be an entity in more than one SoS. An SoS is often comprised of existing constituent systems along with new constituent systems which are developed and integrated into the SoS. The focus of this document is a constituent system as the Sol, as is shown in Figure 1. The considerations provided in this document are with respect to what is necessary to account for the life cycle of the constituent system or Sol to enable it to interact in the anticipated SoS configurations.
SoS and constituent systems can apply to any domain. For example, in an air transportation SoS, constituent systems may include the air traffic management systems, airports and aircraft. In a money transfer SoS (see an example in Annex B), constituent systems may include different banks. In a military SoS, weapons, sensors and communication systems may be considered constituent systems. This document addresses the SoS considerations for the life cycle stages of systems (new or evolving) which are constituents of one or more SoS.