Systems and software engineering — Taxonomy of systems of systems

This document defines a normalized taxonomy for systems of systems (SoS) to facilitate communications among stakeholders. It also briefly explains what a taxonomy is and how it applies to the SoS to aid in understanding and communication.

Ingénierie système et logiciel — Taxonomie des systèmes de systèmes

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Published
Publication Date
22-Jul-2019
Current Stage
6060 - International Standard published
Due Date
01-Nov-2019
Completion Date
23-Jul-2019
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INTERNATIONAL ISO/IEC/
STANDARD IEEE
21841
First edition
2019-07
Corrected version
2019-09
Systems and software engineering —
Taxonomy of systems of systems
Ingénierie système et logiciel — Taxonomie des systèmes de systèmes
Reference number
ISO/IEC/IEEE 21841:2019(E)
©
ISO/IEC 2019
©
IEEE 2019

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ISO/IEC/IEEE 21841:2019(E)

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© IEEE 2019
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ii © IEEE 2019 – All rights reserved

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ISO/IEC/IEEE 21841:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 General terms . 1
3.2 SoS types. 2
4 Concepts and application . 3
4.1 Overview . 3
4.2 Importance of taxonomies to SoS . 3
4.3 Use of SoS taxonomies . 3
5 Taxonomies for systems of systems . 4
5.1 General . 4
5.2 Taxa: directed, acknowledged, collaborative and virtual . 4
5.2.1 Overview . 4
5.2.2 Description of the taxa . 4
5.2.3 Examples of potential application of the taxa . 5
5.2.4 When to use . 5
5.2.5 How to use . 5
5.2.6 Why to use . 6
5.2.7 Limitations . 6
5.2.8 Benefits of use . 6
Annex A (informative) Summary of SoS taxonomies . 7
Bibliography . 8
IEEE notices and abstract . 9
© ISO/IEC 2019 – All rights reserved
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ISO/IEC/IEEE 21841:2019(E)

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
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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
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While the IEEE administers the process and establishes rules to promote fairness in the consensus
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iso/ foreword .html.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 7, Systems and software engineering, in cooperation with the Systems and Software
Engineering Standards Committee of IEEE Computer Society, under the Partner Standards Development
Organization cooperation agreement between ISO and IEEE.
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.
This corrected version of ISO/IEC/IEEE 21841:2019 incorporates the following correction:
— The publication date on the cover page has been corrected.
© ISO/IEC 2019 – All rights reserved
iv © IEEE 2019 – All rights reserved

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ISO/IEC/IEEE 21841:2019(E)

Introduction
Systems of systems engineering (SoSE) is a concept that is increasingly thought of as a discipline
important for the realization and sustainability of large and persistent sociotechnical systems in areas
as diverse as healthcare, transportation, energy, defense, corporations, cities and government.
While SoSE applies broadly to hardware, software, middle-ware as well as embedded, cyber-physical
and digital systems, the importance of SoSE has been heightened in the last fifteen years by the rapid
increase in the pervasiveness of information technology (IT), illustrated by new technologies and
paradigms such as Sensor Networks, Cloud Computing, the Internet of Things, Big Data, Smart Devices
and Artificial Intelligence. It is, for instance, the application of these technologies to cities that transform
them into “smarter” cities.
This pervasiveness of IT was not only driven by the availability of these technologies, but also more
importantly by the requirements in our resource and environmentally-constrained world for increased
and sustainable economic development and, ultimately, personal well-being.
SoSE goes well beyond IT and potentially applies to all types of systems, including hardware and
cyber physical systems where IT is an enabler. SoSE addresses functionality, performance and
interdependencies of the systems as well as their connectivity. The interconnectivity of systems has
become pervasive in large command and control systems, defense systems, communications systems,
transportation systems and medical/health systems, among others. The accelerating need to share
information and leverage capabilities from other systems has changed how systems need to be viewed
and engineered.
Taxonomies provide a means in many fields to classify and describe the relationships among the
relevant elements being studied. The elements of a taxonomy, or taxa, form a partitioning or means of
classification within that body of knowledge. In the context of systems of systems (SoS), the relevant
elements of the system of interest are, by definition, systems themselves. Using essential characteristics
to partition the various types of SoS provides an abbreviated nomenclature for thinking about SoS.
Based on taxonomies, different approaches to the engineering of systems of systems are possible,
improving the efficiency and effectiveness of systems of systems engineering.
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INTERNATIONAL STANDARD ISO/IEC/IEEE 21841:2019(E)
Systems and software engineering — Taxonomy of systems
of systems
1 Scope
This document defines a normalized taxonomy for systems of systems (SoS) to facilitate communications
among stakeholders. It also briefly explains what a taxonomy is and how it applies to the SoS to aid in
understanding and communication.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE For additional terms and definitions in the field of systems and software engineering, see
ISO/IEC/IEEE 24765, which is published periodically as a “snapshot” of the SEVOCAB (Systems and software
Engineering Vocabulary) database and is publicly accessible at www .computer .org/ sevocab.
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/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
— IEEE Standards Dictionary Online: available at http:// dictionary .ieee .org
3.1 General terms
3.1.1
constituent system
CS
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 (3.1.3), utilization, goals, and resources, but interacts within
the SoS to provide the unique capability of the SoS.
[SOURCE: ISO/IEC/IEEE 21839:2019, 3.1.1, modified — The abbreviated term "CS" has been added.]
3.1.2
governance
process of establishing and enforcing strategic goals and objectives, organizational policies and
performance parameters
Note 1 to entry: This definition is adapted from Reference [8].
© ISO/IEC 2019 – All rights reserved
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3.1.3
management
system of controls and processes required to achieve the strategic objectives set by the organization's
governing body
Note 1 to entry: Management is subject to the policy guidance and monitoring set through corporate governance
(3.1.2).
[SOURCE: ISO/IEC/IEEE 24765:2017, 3.2338]
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 interaction of the constituent systems in the
system of systems.
[SOURCE: ISO/IEC/IEEE 21839:2019, 3.1.4]
3.1.5
systems of systems engineering
SoSE
process of planning, analyzing, organizing, developing and integrating the capabilities of a mix of
existing and new systems, including inter-system infrastructure, facilities, and overarching processes
into a system-of-systems capability that is greater than the sum of the capabilities of the constituent
systems (3.1.1)
Note 1 to entry: This definition is adapted from Reference [9].
Note 2 to entry: SoSE also includes testing, modification, maintenance and other post-integration activities.
3.1.6
taxonomy
scheme that partitions a body of knowledge and defines the relationships among the pieces
[SOURCE: ISO/IEC/IEEE 24765:2017, 3.4167, modified — Definition 2 has been removed; Note 1 to entry
has been removed.]
3.2 SoS types
3.2.1
acknowledged system of systems
acknowledged SoS
SoS (3.1.4) with recognized objectives, a designated manager, and resources for the SoS
Note 1 to entry: Constituent systems (3.1.1) retain their independent ownership, objectives, funding, and
development and sustainment approaches. Changes in the systems are based on cooperative agreements
between the SoS and the system.
Note 2 to entry: This definition is adapted from Reference [7].
3.2.2
collaborative system of systems
collaborative SoS
SoS (3.1.4) in which component systems interact more or less voluntarily to fulfill agreed-upon central
purposes
Note 1 to entry: Constituent systems (3.1.1) collectively decide how to provide or deny service, thereby providing
means of enforcing and maintaining consistency.
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Note 2 to entry: This definition is adapted from Reference [7].
3.2.3
directed system of systems
directed SoS
SoS (3.1.4) created and managed to fulfill specific purposes and the constituent systems (3.1.1) are
subordinated to the SoS
Note 1 to entry: Component systems maintain an ability to operate independently; however, their normal
operational mode is subordinated to the central managed purpose.
Note 2 to entry: This definition is adapted from Reference [7].
3.2.4
virtual system of systems
virtual SoS
SoS (3.1.4) that lacks a central management (3.1.3) authority and a centrally-agreed-upon purpose
for the SoS
Note 1 to entry: Large-scale behavior emerges—and can be desirable—but this type of SoS relies on relatively
invisible mechanisms to maintain it.
Note 2 to entry: Virtual SoS are typically self-organizing.
Note 3 to entry: This definition is adapted from Reference [7].
4 Concepts and application
4.1 Overview
Taxonomies provide a means in many fields to classify and describe the relationships between the
relevant elements being studied. The elements of a taxonomy, or taxa, form a partitioning or means of
classification within that body of knowledge. Partitioning based on essential characteristics provides
an abbreviated nomenclature to refer to a larger composite of characteristics, facilitating discussion
about the partitions (taxa) without having to refer to each of the characteristics.
4.2 Importance of taxonomies to SoS
In systems engineering (SE), the relevant pieces of the system of interest can be called subsystems,
elements or components. In the context of SoS, the relevant pieces of the system of interest are, by
definition, systems themselves. These are called constituent systems (CS) throughout this document.
That is, an SoS consists of some number of CS, plus any inter-system infrastructure, facilities and
processes necessary to enable the CS to integrate or interoperate. Relationships between CS affect
the SoS. Using essential characteristics to partition the various types of SoS provides an abbreviated
nomenclature for thinking about SoS. While Clause 5 elaborates one mature SoS taxonomy, Annex A
provides a list of SoS less-mature taxonomies. Based on taxonomies, different approaches to the
engineering of systems of systems are possible, improving the efficiency and effectiveness of SoSE.
NOTE 1 Taxonomies can have some overlap in their definition and need not be orthogonal to each other to
be useful. An SoS can be considered as belonging to several taxonomies as long as its characteristics meet the
definitions of the taxonomies.
NOTE 2 It is possible that inter-system infrastructure, facilities and processes do not meet the criteria for
being systems in their own right. From the perspective of the SoS, these could be system elements (or SoS
elements).
4.3 Use of SoS taxonomies
There are many characteristics such as scale and scope, around which taxonomies can be derived. The
SoS taxonomy in Clause 5 organizes the relevant aspects or essential characteristics of SoS, providing
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specific viewpoints that align with stakeholder concerns. This organization facilitates communications
between the various stakeholders that are involved with activities like governance, engineering,
operation and management of these SoS, and provides a reference for other related standards. The
taxonomy in Clause 5 meets the following criteria.
— External references are publicly available.
— The taxa are stable with evidence of having been applied in multiple systems.
Annex A lists additional SoS taxonomies that do not meet all of the above criteria. These developing
taxonomies can still be useful, but they lack sufficient maturity to be included in Clause 5. As the
discipline matures, it is likely that more taxonomies will evolve.
5 Taxonomies for systems of systems
5.1 General
SoS taxonomies organize the relevant aspects or essential characteristics of SoS, providing specific
viewpoints that align with stakeholder concerns. Taxonomies can have some overlap in their
construction, but the lack of orthogonality does not inhibit their application.
Since most of the taxonomies are not explicitly named, they are most often referenced in practice by the
author’s names or the names of the taxa. Consequently, the taxonomies are presented using the taxa
names themselves, using the author’s order.
5.2 Taxa: directed, acknowledged, collaborative and virtual
5.2.1 Overview
In this taxonomy, SoS are classified according to the degree of managerial and operational independence.
Four types are defined: directed, acknowledged, collaborative and virtual.
[6]
This taxonomy is mature, originating in the work of Maier (1998) , expanded by Dahmann and Baldwin
[9]
(2008) and published as an informative annex in ISO/IEC/IEEE 15288. Maier’s observation was that
SoS are not simply systems in which the constituents are also systems. One essential characteristic
is that constituent systems within the SoS are operationally independent. Operational i
...

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