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.¶

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:¶

• 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.¶

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 a thing or an object as digital twin. The location definitions are on class-level, and describes the use of sdfLocation [I-D.ietf-laari-asdf-sdf-relations].¶

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

  "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"
        }
      }
    }
  ...
  }

  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"
        }
      }
    }
  ...

  sdfObject: {
    "sdfLocation": {
      "sdfData": {
        "geoLocation" : {
            "latitude": "string",
            "longitude": "string"
            "altitude": "string"
        }
          ...
        "Boat_#1": {
            "latitude": "35.5188233791372",
            "longitude": "129.37308376484913",
            "altitude": "0.0"
        }
      }
    }
  }

  sdfObject: {
    "sdfLocation": {
      "sdfData": {
        "geoLocation" : {
            "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. References