ASDF H. Lee, Ed.
Internet-Draft J. Hong
Intended status: Standards Track ETRI
Expires: 8 October 2025 J-S. Youn
Dong-eui Univ
Y-G. Hong
Daejeon University
6 April 2025
Semantic Definition Format (SDF) modeling for Digital Twin
draft-lee-asdf-digital-twin-07
Abstract
This memo specifies SDF modeling for a digital twin, i.e. a digital
twin system, and its Things. An SDF is a format that is used to
create and maintain data and interaction, and to represent the
various kinds of data that is exchanged for these interactions. The
SDF format can be used to model the characteristics, behavior and
interactions of Things, i.e. physical objects, in a digital twin that
contain Things as components.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SDF structure for digital twin . . . . . . . . . . . . . . . 3
4. New Elements for Digital Twin . . . . . . . . . . . . . . . . 4
5. Requirements for digital twin . . . . . . . . . . . . . . . . 7
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Data acquisition . . . . . . . . . . . . . . . . . . . . 7
5.3. Data analysis . . . . . . . . . . . . . . . . . . . . . . 7
5.4. Identification . . . . . . . . . . . . . . . . . . . . . 7
5.5. Accuracy . . . . . . . . . . . . . . . . . . . . . . . . 7
5.6. Synchronization . . . . . . . . . . . . . . . . . . . . . 7
6. Procedures for digital twin . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
A digital twin is defined as a digital representation of an object of
interest and may require different capabilities, for example,
synchronization and real-time support, according to the specific
domain of application. [Y.4600]. Digital twin help organizations
improve important functional objectives, including real-time control,
off-line analytics, and predictive maintenance, by modeling and
simulating objects in the real world. Therefore, it is important for
a digital twin to represent as much real-world information about the
object as possible when digitally representing the object.
Nowadays, digital twin technologies are applied in various domains
including manufacturing, energy, medical, farm, transportation, etc.
And a common format is needed to represent the objects in the domains
as digital twins. SDF [I-D.ietf-asdf-sdf] can be used for modeling
objects as digital twins.
This document specifies the modeling and guidance on how to use SDF
to represent objects as digital twins.
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2. Terminology
This specification uses the terminology specified in
[I-D.ietf-asdf-sdf] in particular "Class Name Keyword", "Object", and
"Affordance".
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. SDF structure for digital twin
This section describes SDF structure with the new Class Name Keyword,
sdfNonAffordance, to represent a thing or an object as a digital
twin. The architecture of a digital twin based on the SDF model is
illustrated in Figure 1, , following the guidelines of [ISO23247-3].
The Physical Layer comprises affordance and non-affordance objects.
From the real-world objects, only those deemed relevant are selected
for representation as digital twins. The Digital Twin Layer is
structured into three sublayers: the Device Communication Sublayer,
the Digital Twin Sublayer, and the Application Sublayer. The Device
Communication Sublayer is responsible for monitoring and collecting
data from both affordance and non-affordance objects. This sublayer
provides the necessary data to synchronize the physical objects with
their digital twin counterparts. The Digital Twin Sublayer ensures
synchronization between the affordance and non-affordance objects and
their respective digital twins using the data provided by the Device
Communication Sublayer. The Application Sublayer presents the
synchronized values of the digital twins to users, facilitating
informed decision-making.
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+---------------------------------------------+ - - - - - - - - - - -
| Application Sublayer |
| +----------+ +------+ +--------+ +--------+ |
| | Human | | HMI | | Apps | | Peers | |
| +----------+ +------+ +--------+ +--------+ |
+---------------------------------------------+
| Digital Twin Sublayer |
| +----------+ +-------------+ +------------+ |
| | Operation| | Application | | Resource | |
| | and | | and | | access and | |
| |management| | service | |interchange | |
| +----------+ +-------------+ +------------+ |
| +-----------------------------------------+ | Digital twin Layer
| | Digital representation of objects | |
| | +-------------+ +----------------+ | |
| | | Affordance | | Non-Affordance | | |
| | | objects | | objects | | |
| | +-------------+ +----------------+ | |
| +-----------------------------------------+ |
+---------------------------------------------+
| Device Communication Sublayer |
| +-------------+ +----------------+ |
| | Data | | Object | |
| | collection | | control | |
| +-------------+ +----------------+ |
+---------------------------------------------+ - - - - - - - - - - -
| +-------------+ +----------------+ |
| | Affordance | | Non-Affordance | |
| | objects | | objects | | Physical Layer
| +-------------+ +----------------+ |
+---------------------------------------------+ - - - - - - - - - - -
Figure 1: Basic Architecture of digital twin
4. New Elements for Digital Twin
The SDF language uses six Class Name Keywords, and sdfNonAffordance
is added as a new Class Name Keyword for digital twin.
The information attributes for digital twin are defined in
[ISO23247-3]. Some of them, for example characteristics and status,
can be described using existing Class Name Keywords. And the others,
for example location, can be described using sdfNonAffordance.
The mapping information attributes of digital twin to qualities of
sdfThing are shown in Table 1. It is required to define a new
quality in sdfThing in order to express the properties of digital
twins such as location.
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+================+=================================+===============+
| Information | Quality | Description |
+================+=================================+===============+
| Idetifier | | A value used |
| | | to uniquely |
| | | identify a |
| | | sdfThing / |
| | | sdfObject |
+----------------+---------------------------------+---------------+
| Characteristic | sdfProperty | A typical or |
| | | noticeable |
| | | feature of a |
| | | sdfThing / |
| | | sdfObject |
+----------------+---------------------------------+---------------+
| Schedule | sdfEvent | Time |
| | | information |
| | | bound to a |
| | | sdfThing / |
| | | sdfObject |
+----------------+---------------------------------+---------------+
| Status | sdfAction | A condition |
| | | of a sdfThing |
| | | / sdfObject |
+----------------+---------------------------------+---------------+
| Location | | Geographical |
| | | or relative |
| | | location |
| | | information |
| | | of a sdfThing |
| | | / sdfObject |
+----------------+---------------------------------+---------------+
| Report | sdfData | Description |
| | | of activities |
| | | done by or |
| | | onto a |
| | | sdfThing / |
| | | sdfObject |
+----------------+---------------------------------+---------------+
| Relationship | [I-D.ietf-laari-asdf-relations] | Connection |
| | | information |
| | | between two |
| | | or more |
| | | sdfThings / |
| | | sdfObjects |
+----------------+---------------------------------+---------------+
Table 1: Mapping Information Attributes of Digital Twin to
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Qualities of sdfThing
{
"info": {
"title": "An example of the heater #1 in the boat #007",
"version": "2025-01-27",
"copyright": "Copyright 2025. All rights reserved.",
},
"namespace": {
"heater1": "https://example.com/heater1"
},
"defaultNamespace": "heater1",
"sdfThing": {
"boat": {
"description" : "A boat including heater1",
"sdfProperty": {
"status": {
"description": "The status of the boat #007 ; false for stop and true for move."
"sdfRef": "#/sdfProproperty/status"
}
},
"sdfObject": {
"heater1": {
identifier: {
"UUID": { "a2e06d16-df2c-4618-aacd-490985a3f763" }
}
location:{
"wgs84": {
"latitude": "35.2988233791372",
"longitude": "129.25478376484913",
"altitude": "0.0"
},
"postal": {
"city": "Ulsan",
"post-code": "44110",
"country": "South Korea"
},
"w3w": {
"what3words":"toggle.mopped.garages"
}
}
"sdfData" : {
report: {
"On February 24, 2025, the boat #007's heater #1 was on from 9 a.m. to 6 p.m."
}
}
}
}
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}
}
}
Figure 2: An example of SDF mapping for digital twin
5. Requirements for digital twin
5.1. Overview
A digital twin is a partial representation of sdfThing or sdfObject
that contains attributes such as sdfProperty, sdfAction and
sdfEvent[ISO23247-1]. By representing sdfThing as a digital twin,
crucial events that require appropriate action can be quickly
detected and controlled. The requirements defined in [ISO23247-1]
are applied to represent sdfThings and sdfObjects as digital twins.
5.2. Data acquisition
Data related to sdfThing and sdfObject, such as sdfProperty,
sdfEvent, and sdfAction, should be collected from IP and non-IP
devices.
5.3. Data analysis
The collected data needs to be analyzed to understand the state of
sdfThing and sdfObject.
5.4. Identification
The sdfThings and sdfObjects should contain data that uniquely
identifies them as digital twins.
5.5. Accuracy
The sdfThings and sdfObjects should be represented as digital twins
with appropriate levels of detail and accuracy, depending on the
application.
5.6. Synchronization
The sdfThings and sdfObjects should be synchronized with their
digital twins in real-time as appropriate for the application. Newly
added or removed sdfThings and sdfObjects should be recognized and
reflected in the digital twin.
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6. Procedures for digital twin
A procedure for representing sdfThing, as a digital twin in a domain
is as follows:
* defining a purpose for expressing the observable object, as known
as a physical asset or an object of interest, as a digital twin in
the domain
* organizing data based on the roles of the observable object in the
domain
* configuring the observable object into the digital twin based on
the data for the purposes
* interworking with a digital twin of each of other domains in which
the observable object performs a different role
* synchronizing the observable object and the digital twin
7. Security Considerations
Only authorized users should have the authority to manage sdfThings
and sdfObjects.
8. IANA Considerations
This document has no IANA actions.
9. References
9.1. Normative References
[I-D.ietf-asdf-sdf]
Koster, M., Bormann, C., and A. Keränen, "Semantic
Definition Format (SDF) for Data and Interactions of
Things", Work in Progress, Internet-Draft, draft-ietf-
asdf-sdf-23, 17 March 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-asdf-
sdf-23>.
[I-D.ietf-laari-asdf-relations]
Laari, P., "Extended relation information for Semantic
Definition Format (SDF)", Work in Progress, Internet-
Draft, I-D.ietf-laari-asdf-relations-04, 28 January 2025,
<https://datatracker.ietf.org/doc/html/I-D.ietf-laari-
asdf-relations-04>.
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[ISO23247-1]
"Automation systems and integration Digital twin framework
for manufacturing - Part 1: Overview and general
principles, ISO 23247-1.", October 2021,
<https://www.iso.org/standard/75066.html>.
[ISO23247-3]
"Automation systems and integration Digital twin framework
for manufacturing - Part 3: Digital representation of
manufacturing elements, ISO 23247-3.", October 2021,
<https://www.iso.org/standard/78744.html>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[Y.4600] Union, I. T., ""Recommendation ITU-T Y.4600 (2022),
Requirements and capabilities of a digital twin system for
smart cities.", August 2022.
9.2. Informative References
[saref4bldg]
Poveda-Villaln, M. and R. Garcia-Castro, "SAREF extension
for building", 5 June 2020,
<https://saref.etsi.org/saref4bldg>.
Authors' Addresses
Hyunjeong Lee (editor)
Electronics and Telecommunications Research Institute
218 Gajeong-ro, Yuseong-gu
Daejeon
34129
South Korea
Phone: +82 42 860 1213
Email: hjlee294@etri.re.kr
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Jungha Hong
Electronics and Telecommunications Research Institute
218 Gajeong-ro, Yuseong-gu
Daejeon
34129
South Korea
Phone: +82 42 860 0926
Email: jhong@etri.re.kr
Joo-Sang Youn
DONG-EUI University
176 Eomgwangno Busan_jin_gu
Busan
47340
South Korea
Phone: +82 51 890 1993
Email: joosang.youn@gmail.com
Yong-Geun Hong
Daejeon University
62 Daehak-ro, Dong-gu
Daejeon
34520
South Korea
Phone: +82 42 280 4841
Email: yonggeun.hong@gmail.com
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