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

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 . 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 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.

Terminology This specification uses the terminology specified in 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 when, and only when, they appear in all capitals, as shown here.

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 .

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 , we can use the following namespace definition:. { "namespace": { "saref": "https://saref.etsi.org/saref4bldg/v1.1.2/" } }

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

The locationType quality describes the type of location including geographical or relative information . 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.

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" } } } ... }

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

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

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 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" } } } ...

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