Internet-Draft SDF for Digital Twin October 2023
Lee, et al. Expires 25 April 2024 [Page]
Workgroup:
ASDF Working Group
Internet-Draft:
draft-lee-asdf-digital-twin-00
Published:
Intended Status:
Standards Track
Expires:
Authors:
HJ. Lee
ETRI
J-S. Youn
Dong-eui Univ
Y-G. Hong
Daejeon University

Extended information of Semantic Definition Format (SDF) for Digital Twin

Abstract

An SDF specification can describe the definition of a Things, i.e., physical objects and their associated interactions and express the various information that be exchanged for the interactions. Therefore, the SDF format can be used to define the behaviour of an object and its associated data model and interaction model in a digital twin system that has an object as a component. In a digital twin system, interactions between physical and virtual objects, as well as interactions of objects existing in the different digital twin systems, are performed over a network, which is important to provide location information of objects during interactions. This document specifies the extension information of SDF to represent the location information of an objects.

Status of This Memo

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This Internet-Draft will expire on 25 April 2024.

Table of Contents

1. Introduction

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, predictive maintenance by modelling and simulating of 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:

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.

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 Location Extension for Digital Twin

This section defines a new SDF Class Name Keyword, sdfLocation, that can be used to represent the location of an object as digital twin. The location definitions are on class-level, and describes the use of sdfLocation [I-D.laari-asdf-relations].

3.1. Namespaces

The SDF namespace block can be used to provide CURIE prefixes for external ontologies for use with sdfLocation extension. For example, in case of SAREF (Smart Applications REFerence ontology) ontology extension for buildings [saref4bldg], we can use the following namespace definition:.

{
    "namespace": {
     "saref": "https://saref.etsi.org/saref4bldg/v1.1.2/"
    }
}

3.2. Qualities of sdfLocation

This section defines the qualities of the sdfLocation. These qualities are used to define the potential type of the sdfLocation.

Table 1: Qualities of sdfLocation
Quality Type Required Description
locationType string yes What kind of location these definitions have
target string no Target model for the location
description string no Description of the location
label string no Short text describing the location
property object no Additional properties for this location
$comment string no Additional comments for implementors

3.2.1. locationType

The locationType quality describes the type of location including geographical or relative information [ISO23247-3]. This can use different descriptions, such as GPS, postal address, relative location. The purpose of the locationType is to represent the current location of an sdfThing or an sdfObject. For example, the locationType can be defined as "218 Gajeong-ro, 7th building in ETRI, WorkUnit #3 in ETRI branch #2" and so on.

3.2.2. 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.

  "namespace": {
    "exont": "https://example.com/relationOntology",
    "saref": "https://saref.etsi.org/core/v3.1.1/"
  },
  sdfObject: {
    "Humidity": {
      "description": "Example Humidity object",
      "sdfProperty": {
        ...
      },
      "sdfLocation": {
        "postalAddr": {
            "locationType": "exont:postal-addr",
            "target": "saref:PostalAddress",
            "description": "address of object",
            "label":"postcode"
        }
      }
    }
  ...
  }

3.2.3. description

The "description" field defines the location. For SDF version 1.1, the description is a string.

3.2.4. label

Short text describing the location, similar to label quality in other SDF definitions.

3.3. Example location description with sdfType links

This extension allows you to describe location from the SDF model to various (SDF or other) definitions. For link data types for affordance, for example, for link properties that can be accessed and modified during runtime, the "sdfType for links" extension [I-D.bormann-asdf-sdftype-link] can be used instead. In the following example, we have a definition for location with the postal address format:

  sdfObject: {
    "example-object": {
      "description": "example object",
      "sdfProperty": {
        ...
      },
      "sdfLocation": {
        "postalAddr": {
            "locationType": "exont:postal-addr",
            "target": "saref:PostalAddress",
            "description": "Postal address of a company", "218 Gajeong-ro ...",
            "label":"34129",
            "property":"company address"
        }
      }
    }
  ...

4. Security Considerations

TODO Security

5. IANA Considerations

This document has no IANA actions.

6. References

6.1. Normative References

[Y.4600]
Union, I. T., ""Recommendation ITU-T Y.4600 (2022), Requirements and capabilities of a digital twin system for smart cities.", .
[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-16, , <https://datatracker.ietf.org/doc/html/draft-ietf-asdf-sdf-16>.
[I-D.laari-asdf-relations]
Laari, P., "Extended relation information for Semantic Definition Format (SDF)", Work in Progress, Internet-Draft, draft-laari-asdf-relations-02, , <https://datatracker.ietf.org/doc/html/draft-laari-asdf-relations-02>.
[ISO23247-3]
"Automation systems and integration Digital twin framework for manufacturing - Part 3: Digital representation of manufacturing elements, ISO 23247-3.", , <https://www.iso.org/standard/78744.html>.
Bormann, C., "An sdfType for Links", Work in Progress, Internet-Draft, draft-bormann-asdf-sdftype-link-01, , <https://datatracker.ietf.org/doc/html/draft-bormann-asdf-sdftype-link-01>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <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, , <https://www.rfc-editor.org/rfc/rfc8174>.

6.2. Informative References

[saref4bldg]
Poveda-Villaln, M. and R. Garcia-Castro, "SAREF extension for building", , <https://saref.etsi.org/saref4bldg>.

Authors' Addresses

Hyunjeong Lee
Electronics and Telecommunications Research Institute
218 Gajeong-ro, Yuseong-gu
Daejeon
34129
South Korea
Joo-Sang Youn
DONG-EUI University
176 Eomgwangno Busan_jin_gu
Busan
47340
South Korea
Yong-Geun Hong
Daejeon University
62 Daehak-ro, Dong-gu
Daejeon
34520
South Korea