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The International Organization for Standardization (ISO) has published over 22,000 formal standards supporting the dissemination of good practice to a range of sectors from agriculture to retail.  Due to the breadth of topics covered it is difficult to conceive of a domain which hasn’t been at least partially standardized.  In fact, as of 2019, ISO had four standards published which referenced digital twins:

  • ISO 14033 (Quantitative Environmental Information)
  • ISO 15704 (Requirements for enterprise-referencing architectures)
  • ISO 18101-1 (Oil and Gas interoperability)
  • ISO 30146 (Smart City ICT Indicators)


And, more interestingly, one of these saw the first definition for a digital twin included within an ISO document:


Within ISO, there are several requirements which need to be conformed to when producing a definition.  These requirements are outlined within two standards:

  • ISO 10241-1 (general requirements and examples of presentation)
  • ISO 704 (principles and methods)

ISO 10241-1, which covers the structure of a term including how to structure a definition and referencing; and ISO 704, which covers the principles of doing terminology work.  These standards state that when developing a definition, it should:

  • Be a single phrase specifying the concept and, if possible, representing that concept within a larger system;

The digital twin definition from ISO/TS 18001 does so by referencing other key terms such as digital assets and services.  This provides a relationship to other related terms.  In doing so, this definition makes digital twin a type of digital asset being used to create value.

  • Be general enough to cover the use of the term elsewhere;

This definition is specific enough to capture what a digital twin is in a generalist sense, while also being sufficiently generic that the same definition can be used in other standards.  This is vital to achieve a harmonization of concepts across a disparate suite of documentation.

  • Not include any requirements; and

In addition, this definition doesn’t say what needs to be done for something to be considered a digital twin.  This is important as definitions are meant to inform, not instruct.

  • Be able to substitute the term within a sentence.

Finally, and possibly the most challenging requirement, a definition needs to be able to substitute for the term within a sentence.  For example:

Within the Gemini Principles, there is also another definition to consider:


digital twin
a realistic digital representation of assets, processes or systems in the built or natural environment

However, while this definition isn’t suitable for ISO as it wasn’t designed to meet these requirements, the inclusion of “realistic digital representation” might help enhance the ISO definition.


And there we have it.  The ISO definition for digital twin is, technically speaking, a good example of an ISO definition.  However, does the definition sufficiently capture the correct concepts and relationships outlined within the Gemini Principles?  Following the criteria above, how would you define a digital twin?

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In IEC Smart Cities Systems Committee we are working on a definition from our perspective. Our draft is:

Digital Twin

formal, explicit, computer-readable and computer-executable digital representation of an object or system that allows a computer to understand that object or system

Note 1

Digital twins can be made of material objects and systems (house, city, human, electrical distribution system etc.) and of immaterial objects (process, project plan, etc.)

Note 2

Digital twins can be primary, when the digital representation is developed before the physical object or system is built to help in the design or construction of that object or system. Or they can be secondary, when they are developed to represent an object or system that already exists in the physical world.

Note 3

A digital twin of an existing object or system is created from data gathered from Internet of Things (IoT) sensors, with scientific and social-science modelling, machine learning and other advanced analytics applied to replicate the behaviour of that object or system, supporting decision making.

Note 4

A digital twin of an existing object or system is more than just a model: it must have a two-way connection with that object or system and should provide dynamic as well as static representations of that object or system. Data needs to flow between the physical twin and the digital, enabling insights and creating the opportunity for positive interventions within the physical twin.

Clearly Note 4 has some "should"s in it, so we need to correct this!

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  • 1 year later...

@DRossiter87, thank you for this post. Your explanation of the requirements for a definition to meet the ISO criteria are very helpful. I would like to approach this topic more from the perspective of the business use case and the purpose of the digital twin. Although the ISO/TS 18101:2019 captures certain aspects of the digital twin, I would argue that it doesn't fully capture what a digital twin is. I think the definition of the digital twin should be driven by the purpose one wants to achieve with it. One could argue that a "digital asset on which services can be performed that provide value to an organization" is a CAD or a BIM-file (digital asset) that is used to export drawings in PDF (services) is a digital twin. From my point of view a BIM in and of itself is not a digital twin. However, the data from BIM can used to create a digital twin. As an asset owner I often have discussions with architects about digital twins and design engineers often confuse the concept of a digital twin with BIM.

  • I would say that the power of the digital twin is the ability for the digital representation of the physical object to connect to it's physical environment through a function of input and/or outputs e.g. by geographically referencing the model and using meteorological data to perform simulations.
  • In the operational phase, when the asset owner receives the AIM (according to ISO 19650), the AIM is not yet a digital twin. It's only when the asset owner connects the digital representation of the object to its physical environment that it actually becomes a digital twin. That could be achieved by e.g. connecting the AIM to an IoT-platform using data from sensors, booking systems etc.

With these criteria in mind I would propose the following definition "A digital representation of a physical object and its interactions with the environment that creates valuable information."

What do you think?

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