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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 21 April 2025. Lee, et al. Expires 21 April 2025 [Page 1] Internet-Draft SDF for Digital Twin October 2024 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/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. 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 Lee, et al. Expires 21 April 2025 [Page 2] Internet-Draft SDF for Digital Twin October 2024 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. Lee, et al. Expires 21 April 2025 [Page 3] Internet-Draft SDF for Digital Twin October 2024 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| |-------| `-------' Lee, et al. Expires 21 April 2025 [Page 4] Internet-Draft SDF for Digital Twin October 2024 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]. Lee, et al. Expires 21 April 2025 [Page 5] Internet-Draft SDF for Digital Twin October 2024 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 Lee, et al. Expires 21 April 2025 [Page 6] Internet-Draft SDF for Digital Twin October 2024 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". Lee, et al. Expires 21 April 2025 [Page 7] Internet-Draft SDF for Digital Twin October 2024 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. Lee, et al. Expires 21 April 2025 [Page 8] Internet-Draft SDF for Digital Twin October 2024 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. Lee, et al. Expires 21 April 2025 [Page 9] Internet-Draft SDF for Digital Twin October 2024 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. Lee, et al. Expires 21 April 2025 [Page 10] Internet-Draft SDF for Digital Twin October 2024 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, . Lee, et al. Expires 21 April 2025 [Page 11] Internet-Draft SDF for Digital Twin October 2024 [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, . [ISO23247-1] "Automation systems and integration Digital twin framework for manufacturing - Part 1: Overview and general principles, ISO 23247-1.", October 2021, . [ISO23247-3] "Automation systems and integration Digital twin framework for manufacturing - Part 3: Digital representation of manufacturing elements, ISO 23247-3.", October 2021, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . Authors' Addresses Hyunjeong Lee (editor) Electronics and Telecommunications Research Institute 218 Gajeong-ro, Yuseong-gu Daejeon 34129 South Korea Phone: +82 42 860 1213 Lee, et al. Expires 21 April 2025 [Page 12] Internet-Draft SDF for Digital Twin October 2024 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 Lee, et al. Expires 21 April 2025 [Page 13]