Systems and software engineering -- System of systems (SoS) considerations in life cycle stages of a system

1.1 Purpose This document provides a set of critical system of systems (SoS) considerations to be addressed at key points in the life cycle of the system of interest (SoI). This document refers to considerations that apply to an SoI that is a constituent system that interacts in an SoS. The considerations and life cycle model align with those which are already defined in ISO/IEC/IEEE 15288 and ISO/IEC/IEEE 24748-1. Selected subsets of these considerations can be applied throughout the life of systems through the involvement of stakeholders. The ultimate goal is to achieve customer satisfaction, so that when delivered, the SoI will operate effectively in the operational or business environment which is typically characterized as one or more systems of systems. This document concerns those systems that are man-made and are configured with one or more of the following: hardware, software, humans, procedures and facilities. 1.2 Field of application This document addresses SoS considerations that apply to systems at each stage of their respective life cycles. There is a wide variety of systems in terms of their purpose, domain of application, complexity, size, novelty, adaptability, quantities, locations, life spans and evolution. This document is concerned with describing the system of systems considerations that apply to a system that is the SoI; that is a constituent system within a system of systems. It applies to one-of-a-kind systems, mass produced systems or customized, adaptable systems. 1.3 Limitations This document does not detail the approach to addressing system of systems considerations in terms of methods or procedures. This document does not detail the described documentation in terms of name, format, explicit content and recording media of documentation.

Ingénierie du logiciel et des systèmes -- Études du système des systèmes (SdS) dans les étapes du cycle de vie d'un système

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INTERNATIONAL ISO/IEC/
STANDARD IEEE
21839
First edition
2019-07
Systems and software engineering —
System of systems (SoS) considerations
in life cycle stages of a system
Ingénierie du logiciel et des systèmes — Études du système des
systèmes (SdS) dans les étapes du cycle de vie d'un système
Reference number
ISO/IEC/IEEE 21839:2019(E)
ISO/IEC 2019
IEEE 2019
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ISO/IEC/IEEE 21839:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2019
© IEEE 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
© ISO/IEC 2019 – All rights reserved
ii © IEEE 2019 – All rights reserved
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ISO/IEC/IEEE 21839:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

1.1 Purpose .......................................................................................................................................................................................................... 1

1.2 Field of application .............................................................................................................................................................................. 1

1.3 Limitations .................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms, definitions and abbreviated terms ................................................................................................................................ 1

3.1 Terms and definitions ....................................................................................................................................................................... 1

3.2 Abbreviated terms ............................................................................................................................................................................... 2

4 Concepts ........................................................................................................................................................................................................................ 3

4.1 System of systems................................................................................................................................................................................. 3

4.2 Constituent systems ........................................................................................................................................................................... 3

4.3 System life cycle stages .................................................................................................................................................................... 4

4.4 SoS technical base ................................................................................................................................................................................ 6

5 System of systems considerations in SoI life cycle stages .......................................................................................... 6

5.1 SoS considerations in the Concept Stage .......................................................................................................................... 6

5.1.1 General...................................................................................................................................................................................... 6

5.1.2 Concept stage capability considerations ..................................................................................................... 6

5.1.3 Concept Stage technical considerations ...................................................................................................... 9

5.1.4 Concept Stage management considerations .........................................................................................11

5.2 Addressing SoS considerations in the development stage .............................................................................12

5.2.1 General...................................................................................................................................................................................12

5.2.2 Development stage capability considerations.....................................................................................12

5.2.3 Development stage technical considerations .................. .....................................................................15

5.2.4 Development stage management considerations ............................................................................17

5.3 Addressing SoS considerations during the production stage ......................................................................19

5.4 Addressing SoS considerations during utilization and support stages ...............................................20

5.4.1 General...................................................................................................................................................................................20

5.4.2 Utilization and support stage capability considerations............................................................20

5.4.3 Utilization and support stage technical considerations .................. ............................................23

5.4.4 Utilization and support stage management considerations ...................................................24

5.5 Addressing SoS considerations in retirement stage ............................................................................................24

Annex A (informative) System of systems technical base ............................................................................................................27

Annex B (informative) Example SoS considerations in the life cycle stages of a constituent

system ...........................................................................................................................................................................................................................28

Annex C (informative) Relationship to other standards ...............................................................................................................30

Bibliography .............................................................................................................................................................................................................................31

IEEE notices and abstract ............................................................................................................................................................................................32

© ISO/IEC 2019 – All rights reserved
© IEEE 2019 – All rights reserved iii
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ISO/IEC/IEEE 21839:2019(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical

Commission) form the specialized system for worldwide standardization. National bodies that

are members of ISO or IEC participate in the development of International Standards through

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The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

rules given in the ISO/IEC Directives, Part 2 (see www .iso .org/directives).

IEEE Standards documents are developed within the IEEE Societies and the Standards Coordinating

Committees of the IEEE Standards Association (IEEE-SA) Standards Board. The IEEE develops its

standards through a consensus development process, approved by the American National Standards

Institute, which brings together volunteers representing varied viewpoints and interests to achieve the

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While the IEEE administers the process and establishes rules to promote fairness in the consensus

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the information contained in its standards.

Attention is drawn to the possibility that some of the elements of this document may be the subject

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list of patent declarations received (see http: //patents .iec .ch).

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For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso

.org/iso/foreword .html.

ISO/IEC/IEEE 21839 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,

Subcommittee SC 7, Software and systems engineering, in cooperation with the Systems and Software

Engineering Standards Committee of the IEEE Computer Society, under the Partner Standards

Development Organization cooperation agreement between ISO and IEEE.

ISO/IEC/IEEE 21839 is one of three standards dealing with systems of systems. The relationship among

the three standards is described in Annex C.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/members .html.
© ISO/IEC 2019 – All rights reserved
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INTERNATIONAL STANDARD ISO/IEC/IEEE 21839:2019(E)
Systems and software engineering — System of systems
(SoS) considerations in life cycle stages of a system
1 Scope
1.1 Purpose

This document provides a set of critical system of systems (SoS) considerations to be addressed at key

points in the life cycle of the system of interest (SoI). This document refers to considerations that apply

to an SoI that is a constituent system that interacts in an SoS. The considerations and life cycle model

align with those which are already defined in ISO/IEC/IEEE 15288 and ISO/IEC/IEEE 24748-1. Selected

subsets of these considerations can be applied throughout the life of systems through the involvement

of stakeholders. The ultimate goal is to achieve customer satisfaction, so that when delivered, the SoI

will operate effectively in the operational or business environment which is typically characterized as

one or more systems of systems.

This document concerns those systems that are man-made and are configured with one or more of the

following: hardware, software, humans, procedures and facilities.
1.2 Field of application

This document addresses SoS considerations that apply to systems at each stage of their respective

life cycles.

There is a wide variety of systems in terms of their purpose, domain of application, complexity, size,

novelty, adaptability, quantities, locations, life spans and evolution. This document is concerned

with describing the system of systems considerations that apply to a system that is the SoI; that is a

constituent system within a system of systems. It applies to one-of-a-kind systems, mass produced

systems or customized, adaptable systems.
1.3 Limitations

This document does not detail the approach to addressing system of systems considerations in terms of

methods or procedures.

This document does not detail the described documentation in terms of name, format, explicit content

and recording media of documentation.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO/IEC/IEEE 24765, Systems and software engineering — Vocabulary
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions

For the purposes of this document, the terms and definitions in ISO/IEC/IEEE 24765 and the

following apply.
© ISO/IEC 2019 – All rights reserved
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ISO/IEC/IEEE 21839:2019(E)

ISO, IEC and IEEE maintain terminological databases for use in standardization at the following

addresses:
— ISO Online browsing platform: available at https: //www .iso .org/
— IEC Electropedia: available at https: //www .electropedia .org/

— IEEE Standards Dictionary Online: available at https: //ieeexplore .ieee .org/xpls/dictionary .jsp

3.1.1
constituent system
independent system that forms part of a system of systems (SoS) (3.1.4)

Note 1 to entry: Constituent systems can be part of one or more SoS. Each constituent system is a useful system

by itself, having its own development, management, utilization, goals, and resources, but interacts within the SoS

to provide the unique capability of the SoS.
3.1.2
life cycle

evolution of a system, product, service, project or other human-made entity from conception through

retirement
[SOURCE: ISO/IEC/IEEE 15288:2015, 4.1.23]
3.1.3
system of interest
SoI
system whose life cycle is under consideration in the context of this document

[SOURCE: ISO/IEC/IEEE 15288:2015, 4.1.48, modified — the abbreviated term "SoI" has been added;

“this International Standard” has been replaced with “this document”.]
3.1.4
system of systems
SoS

set of systems or system elements that interact to provide a unique capability that none of the constituent

systems (3.1.1) can accomplish on its own

Note 1 to entry: System elements can be necessary to facilitate the interaction of the constituent systems in the

system of systems.
3.1.5
stage

period within the life cycle of an entity that relates to the state of its description or realization

Note 1 to entry: As used in this document, stages relate to major progress and achievement milestones of the

entity through its life cycle.
Note 2 to entry: Stages often overlap.

[SOURCE: ISO/IEC/IEEE 15288:2015, 4.1.43, modified — “this International Standard” has been

replaced with “this document”.]
3.2 Abbreviated terms
SoI system of interest
SoS system of systems
SoSE system of systems engineering
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ISO/IEC/IEEE 21839:2019(E)
4 Concepts
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

[5]

system-of-systems regardless of the complexity or geographic distribution of its components .

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 SoI, 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 SoI to enable it to interact in the

anticipated SoS configurations.
Figure 1 — Focus of the document is on the constituent system in an SoS
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ISO/IEC/IEEE 21839:2019(E)

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.
4.3 System life cycle stages

As a system of systems evolves, each constituent system follows the representative life cycle stages

for its own evolution. The representative life cycle stages are shown in Figure 2. These stages may be

implemented in different progression with iteration and recursion possible, one example of which is

shown in Figure 3. Table 1 summarizes the main purpose of each life cycle stage and shows decision

options common across all life cycle stages.
NOTE See ISO/IEC/IEEE 24748-1:2018, Figure 6.
Figure 2 — Life cycle stages
NOTE See ISO/IEC/IEEE 24748-1:2018, Figure 7.
Figure 3 — Possible progress of life cycle stages
© ISO/IEC 2019 – All rights reserved
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ISO/IEC/IEEE 21839:2019(E)
Table 1 — Life cycle stages, their purposes and decisions options
Life cycle
Purpose Decision options
stages
Identify stakeholders' needs
Concept Explore concepts
Propose viable solutions
— Begin subsequent
Refine system requirements
stage or stages
Create solution description
Development — Continue this
Build system
stage
Verify and validate system
— Go to or restart a
Produce systems
preceding stage
Production
Inspect and test
— Hold project
Operate system to satisfy
activity
Utilization
users' needs
— Terminate project
Provide sustained system
Support
capability
Store, archive or dispose of
Retirement
system
NOTE See ISO/IEC/IEEE 24748-1:2018, Table 1.

In this document, system of systems considerations are addressed at each of these stages for a system

of interest that is intended to interact with other systems (a constituent system of an SoS) as shown

in Figure 3. The stages are addressed as follows: Concept (5.1), Development (5.2), Production (5.3),

Utilisation and Support (5.4) and Retirement (5.5).

As the focus of this document is the life cycle of the constituent system as the system of interest,

SoS considerations to be addressed in each stage in the life cycle of a system are presented as a list

of questions along with the supporting material. SoS considerations are grouped into three areas:

Capability, Technical and Management (including schedule and cost). The document addresses both the

benefit to the system of addressing these SoS questions and the risks of failing to address the questions.

It identifies the type of information or artifacts that provide the information needed to address the

questions and potential actions.
In this document, each stage presents three areas to consider:

— Capability considerations: In this document, capability refers to the ability to achieve overall user

objectives in a mission or business context. User capabilities are often based on the collective effects

of multiple physical systems (referred to as “material”) as well as other factors beyond the systems

themselves (training, procedures, etc. which are referred to in this document as “non-material”).

Typically, the development of an SoI begins with a user need based on an identified gap in capability

and a proposed SoI that focuses on filling that capability gap. From the earliest point in its life cycle,

understanding the role of the SoI in supporting the needed capability is a key concern, particularly

understanding: 1) how the SoI is envisaged to function in the operational or business context, 2)

the constraints that context places on the SoI, and 3) the relationships, interfaces and dependencies

between the SoI and other systems supporting the capability. Relevant ISO/IEC/IEEE 15288

processes are Business or Mission Analysis and Stakeholder Needs and Requirements Definition.

— Technical considerations: As alternative approaches to the SoI are evaluated, consider the

technical impact on external stakeholders and external systems and infrastructure. This includes

both systems/services on which the SoI depends and systems/services that depend on the SoI. Once

these have been identified, assess the ability to influence resource changes in associated systems,

infrastructure or nonmaterial factors. Consider any constraints on the SoI imposed by its SoS

context in selecting the system solution. As the SoI life cycle moves into requirements definition

and design, the technical considerations play a larger role. Understanding these early and factoring

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ISO/IEC/IEEE 21839:2019(E)

them into the technical planning process can be key to successful delivery of both the SoI and the

capability it enables. Relevant ISO/IEC/IEEE 15288 processes are all the Technical processes.

— Management considerations: Consider management issues when dependencies resulting from

interactions need to be negotiated with other systems involved (e.g., interfaces, new or changed

functionality in other systems). If there is an entity with some type of responsibility that spans

an SoS, establish management arrangements with that entity. SoS-related cost and schedule

considerations need to be addressed, including identifying costs and schedules associated with

external systems. Finally, mechanisms should be in place to monitor the progress in the areas of

cross-system dependencies for a prompt identification of any changes or delays which could mean

added cost and time. Plans need to be formulated to accommodate these if necessary. Relevant

ISO/IEC/IEEE 15288 processes are all the Technical Management processes and all the Agreement

processes.

In this document, certain considerations need to be addressed at multiple stages, so if a question also

applies to more than one stage, this is noted.

A system may interact as part of one or more SoS in support of multiple capabilities. In this document,

when the interaction of a system with an SoS is discussed, this may include one or more SoS in support

of one or more capabilities. Thus, although the terms SoS, capability and context are used in singular

form throughout this document, each use can be plural if applicable to the situation.

4.4 SoS technical base

Annex A presents what is termed the “SoS technical base”, which reflects the type of SoS level

technical information that would ideally be available as a reference to an SoI in addressing wider

SoS considerations. As is shown in Figure 1, this document applies to a constituent SoI in an SoS. The

SoS technical base information in Annex A may be available to provide reference information used to

address the SoS considerations and help ensure that organizations responsible for constituent systems

in the SoS can address these considerations in a consistent manner and reduce risks at both the system

and the SoS levels. It is recognized that in many cases, this information may not be available, putting an

added burden on the SoI to address the SoS considerations across the multiple organizations.

5 System of systems considerations in SoI life cycle stages
5.1 SoS considerations in the Concept Stage
5.1.1 General

This subclause describes the SoS considerations for the SoI to be addressed in the Concept Stage as

defined in ISO/IEC/IEEE 24748-1:2018, 5.2. Details of the Concept Stage from ISO/IEC/IEEE 24748-1 are

shown in Box 1.
5.1.2 Concept stage capability considerations

Upon entry into the Concept Stage, evaluate all available information that is relevant to help understand

the user capability needs and identify information gaps. In particular, address questions concerning the

understanding of the capability being sought, and the context of that user capability need, including,

but not limited to:

— Has the operational or business context of the user capability need been described?

— Has the existing user capability been described, including the systems or SoS that currently support

that capability?

— How would a new system which might address the gap fit into current operations or business

processes?
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— If a new system were to be considered, have interfaces with or required changes to current systems

or systems which are planned or in development been identified?

Identifying and addressing constraints are key to effective solutions. An early description of the SoS

context and its potential impact on requirements and dependencies for the SoI provide a solid basis for

the development of a system that can meet user needs, including quality characteristics.

Potential changes to other systems, interfaces and infrastructure need to be identified as early as

possible. This will allow time for multi-lateral SoS trade-off analyses, considering which changes

should be implemented or where they can best be implemented and allow time for negotiations and

organizational agreements to be put in place. Early identification of dependencies between developing

or planned systems provides the opportunity to help ensure that interoperability is maintained despite

changes. An early understanding of these factors can contribute to a sound solution selection for the SoI

and an assessment of SoS risks. This is particularly important for any long-lead items.

Understanding of current operations, business processes and life cycle support is also important to

set the context for the SoI. This includes systems currently supporting the SoS capability, systems in

development or planned and any non-material elements. Consider the full impact of alternatives in

the assessment of possible approaches for addressing the gap(s), including any required changes to

operations, business processes or life cycle support to avoid unwanted effects on other capabilities.

During the Concept Stage, there is a set of questions concerning th
...

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