Extended information of Semantic Definition Format (SDF) for Digital Twin
draft-lee-asdf-digital-twin-04
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| Document | Type | Active Internet-Draft (asdf WG) | |
|---|---|---|---|
| Authors | Hyunjeong Lee , Joo-Sang Youn , Yong-Geun Hong | ||
| Last updated | 2024-10-18 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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draft-lee-asdf-digital-twin-04
ASDF Working Group H. Lee, Ed.
Internet-Draft ETRI
Intended status: Standards Track J-S. Youn
Expires: 21 April 2025 Dong-eui Univ
Y-G. Hong
Daejeon University
18 October 2024
Extended information of Semantic Definition Format (SDF) for Digital
Twin
draft-lee-asdf-digital-twin-04
Abstract
An SDF specification can describe the definition of Things, i.e.,
physical objects and their associated interactions, and express the
various information that is exchanged for these interactions.
Therefore, the SDF format can be used to define the behavior of an
object and its associated data model and interaction model in a
digital twin system that includes the object as a component. In a
digital twin system, interactions between physical and virtual
objects, as well as interactions of objects existing in different
digital twin systems, are performed over a network, making it
important to provide location information of objects during
interactions. This document specifies the extension of SDF to
represent the location information of objects.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 21 April 2025.
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Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. SDF extension for digital twin . . . . . . . . . . . . . . . 4
3.1. SDF extension for location . . . . . . . . . . . . . . . 4
3.2. Architecture of Digital Twin . . . . . . . . . . . . . . 5
4. Qualities of sdfLocation . . . . . . . . . . . . . . . . . . 7
4.1. locationType . . . . . . . . . . . . . . . . . . . . . . 7
4.2. target . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3. description . . . . . . . . . . . . . . . . . . . . . . . 8
4.4. label . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Examples of Location description . . . . . . . . . . . . . . 8
5.1. Postal address . . . . . . . . . . . . . . . . . . . . . 8
5.2. Geographical information . . . . . . . . . . . . . . . . 9
5.3. Relative information . . . . . . . . . . . . . . . . . . 9
6. Requirements for digital twin . . . . . . . . . . . . . . . . 10
6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 10
6.2. Data acquisition . . . . . . . . . . . . . . . . . . . . 10
6.3. Data analysis . . . . . . . . . . . . . . . . . . . . . . 11
6.4. Identification . . . . . . . . . . . . . . . . . . . . . 11
6.5. Accuracy . . . . . . . . . . . . . . . . . . . . . . . . 11
6.6. Synchronization . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
A digital twin is a digital representation of an object of interest
and may require different capabilities (e.g., synchronization, real-
time support) according to the specific domain of application.
[Y.4600]. Digital twin systems 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 system to represent as much real-world information about the
object as possible when digitally representing the object. A
procedure for representing an observable Thing, as known as a
physical asset or an object of interest, as a digital twin in a
domain is as follows:
* defining a purpose for expressing the observable object 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
Nowadays, digital twin systems are applied in various domains
including medical, manufacturing, farm, transportation, etc. And a
common format is needed to represent the objects in the domains as
digital twins. An SDF specification [I-D.ietf-asdf-sdf] can be used
for the purpose of digital representation of objects in a digital
twin system. However, because the SDF specification only provides a
basic model for digital representation, it cannot represent objects
location information.
The location information of the object is the important information
to digitally representation of the object. This document extends the
basic SDF specification by adding a new keyword "location" to
represent an object as a digital twin. This new keyword is needed to
adequately represent the current location of the object, which is
helpful for users to manage the domain efficiently.
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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 extension for digital twin
This section defines a new SDF Class Name Keyword, sdfLocation, that
can be used to represent the location of a thing or an object as a
digital twin. The location definitions are at the class level and
describe the use of sdfLocation. [I-D.ietf-laari-asdf-relations].
3.1. SDF extension for location
The SDF language uses seven predefined Class Name Keywords, including
sdfLocation, for modeling connected Things, as illustrated in
Figure 1. The sdfLocation is a new Class Name Keyword and is used to
describe physical or logical location of sdfThing or sdfObject.
,--------.
|sdfThing|
|--------|
`--------'
,---------.
|sdfObject|
|---------|
`---------'
,-----------. ,---------. ,--------. ,-----------.
|sdfProperty| |sdfAction| |sdfEvent| |sdfLocation|
|-----------| |---------| |--------| |-----------|
`-----------' `---------' `--------' `-----------'
|
,-------.
|sdfData|
|-------|
`-------'
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Figure 1: Add SdfLocation to SDF Models
The sdfLocation is described using conventional GPS coordinates or
postal addresses for physical locations, which enable extensive reuse
and interoperability. The sdfLocation is also described by strings
or integers for relative locations. Using the example in the
[[I-D.ietf-asdf-sdf]], a heater in a boat model can be described as
being on a "boat" using GPS coordinates or in a "specific location on
the boat" using relative locations (Figure 2).
{
"info": {
"title": "Example location of a heater in a boat",
"version": "2024-10-02",
"copyright": "Copyright 2024 digital twin Corp. All rights reserved.",
"license": "https://example.com/license"
},
"namespace": {
"location": "https://example.com/location"
},
"defaultNamespace": "location",
"sdfObject": {
"boat": {
"sdfLocation": {
"wgs84": {
"latitude": "35.2988233791372",
"longitude": "129.25478376484913",
"altitude": "0.0"
},
"postal": {
"city": "Ulsan",
"post-code": "44110",
"country": "South Korea"
},
"w3w": "toggle.mopped.garages"
}
}
}
}
Figure 2: A simple example of an SDF document
3.2. Architecture of Digital Twin
The architecture of a digital twin based on the SDF model is
illustrated in Figure 3, , following the guidelines of [ISO23247-3].
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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.
+---------------------------------------------+ - - - - - - - - - - -
| Application Sublayer |
| +----------+ +------+ +--------+ +--------+ |
| | Human | | HMI | | Apps | | Peer | |
| +----------+ +------+ +--------+ +--------+ |
+---------------------------------------------+
| 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 3: Basic Architecture of digital twin
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In order to send an IPv6 packet over OWC, the packet MUST be passed
down to the LLC sublayer. For IPv6 addressing or address
configuration, the LLC sublayer MUST provide related information,
such as link-layer addresses, to its upper layer.
4. Qualities of sdfLocation
This section defines the qualities of the sdfLocation. These
qualities are used to define the potential type of the sdfLocation.
A named definition entry in an sdfProperty may be associated with
some protocol affordance to enable the application to obtain the
location of sdfThing or sdfObject.
+==============+========+====================================+
| Quality | Type | Description |
+==============+========+====================================+
| (common) | | Section 4.6 in [I-D.ietf-asdf-sdf] |
+--------------+--------+------------------------------------+
| locationType | string | What kind of location these |
| | | definitions have |
+--------------+--------+------------------------------------+
| target | string | Target model for the location |
+--------------+--------+------------------------------------+
| description | string | Description of the location |
+--------------+--------+------------------------------------+
| label | string | Short text describing the location |
+--------------+--------+------------------------------------+
| property | object | Additional properties for this |
| | | location |
+--------------+--------+------------------------------------+
| $comment | string | Additional comments for |
| | | implementors |
+--------------+--------+------------------------------------+
Table 1: Qualities of sdfLocation
4.1. locationType
The locationType quality describes the type of location including
geographical or relative information [ISO23247-3]. This can use
different descriptions, such as geographical information, postal
address, w3w and indoor location. The purpose of the locationType is
to represent the current location of an sdfThing or an sdfObject.
For example, if the locationType is w3w, the location of an object
can be describe as "nutrients.snows.voting".
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4.2. target
The "target" field defines to which definition or ontology term this
definition with sdfLocation has a location to. For example, this can
be #/sdfObject/location, when the target location of an object is
defined in the same SDF model.
sdfObject: {
"Humidity": {
"description": "Example Humidity object",
"sdfProperty": {
...
},
"sdfLocation": {
"postalAddr": {
"locationType": "postalAddr",
"description": "postal address of an object",
"label":"postcode"
}
}
}
...
}
4.3. description
The "description" field specifies the location, which is represented
as a string.
4.4. label
The "label" field is a short text describing the location, similar to
the label quality in other SDF definitions.
5. Examples of Location description
5.1. Postal address
This description allows you to describe location of sdfThing or
sdfObject with postal address.
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sdfObject: {
"example-object": {
"description": "example object",
"sdfProperty": {
...
},
"sdfLocation": {
"postalAddr": {
"locationType": "postalAddr",
"description": "Postal address of a company", "218 Gajeong-ro ...",
"label":"34129"
}
}
}
...
5.2. Geographical information
This description allows you to describe location of sdfThing or
sdfObject with geographical information.
sdfObject: {
"BoatDetector": {
"sdfLocation": {
"wgs84" : {
"latitude": "35.5188233791372",
"longitude": "129.37308376484913",
"altitude": "0.0"
}
}
}
}
5.3. Relative information
This description allows you to describe location of sdfThing or
sdfObject with relative information including geographical
information.
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sdfObject: {
"sdfLocation": {
"wgs84" : {
"latitude": "string",
"longitude": "string"
"altitude": "string"
}
"relativeLocation" : {
"relative-x": "integer",
"relative-y": "integer"
"relative-z": "integer"
"unit":"cm"
}
...
"Boat_#1": {
"latitude": "35.5188233791372",
"longitude": "129.37308376484913",
"altitude": "0.0"
}
"Heater_A_in_the_Boat_#1": {
"latitude": "35.5188233791372",
"longitude": "129.37308376484913",
"altitude": "0.0"
"relative-x": "7215",
"relative-y": "1324"
"relative-z": "217"
}
}
}
6. Requirements for digital twin
6.1. Overview
A digital twin is a partial representation of an sdfThing or
sdfObject including characteristics such as sdfProperty, sdfData, and
sdfLocation[ISO23247-1]. By representing sdfThing and sdfObject as
digital twins, changes that have occurred and require appropriate
action can be quickly detected and controlled. The requirements
defined in [ISO23247-1] can be applied to represent sdfThings and
sdfObjects as digital twins.
6.2. Data acquisition
Data related to sdfThing and sdfObject, such as sdfProperty, sdfData,
and sdfLocation, should be collected from IP and non-IP devices.
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6.3. Data analysis
The collected data needs to be analyzed to understand the state of
sdfThing and sdfObject.
6.4. Identification
The sdfThings and sdfObjects should contain data that uniquely
identifies them as digital twins.
6.5. Accuracy
The sdfThings and sdfObjects should be represented as digital twins
with appropriate levels of detail and accuracy, depending on the
application.
6.6. 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.
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-18, 29 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-asdf-
sdf-18>.
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[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, 20 June 2024,
<https://datatracker.ietf.org/doc/html/I-D.ietf-laari-
asdf-relations>.
[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
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Email: hjlee294@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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