RdfToDtdlConverter sample application to convert RDF to DTDL

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RdfToDtdlConverter is a .NET Core command-line sample application that converts an RDF-based ontology to JSON-LD-based Digital Twins Definition Language (DTDL) version 2 for use by the Azure Digital Twins service.

This sample application accompanies the Converting industry-standard models to DTDL article and demonstrates how to convert an RDF-based model.

It includes a sample Pizza (Turtle) model (WebVOWL) which is used to demonstrate the conversion process. You can use this sample to see the conversion patterns in context, and to have as a building block for your own applications performing model conversions according to your own specific needs.

Features

RdfToDtdlConverter provides the following features:

• Conversion of RDF-based ontology files (Turtle, RDF/XML, etc.) to JSON-LD-based DTDL v2.
• Customizable DTMI prefix
• DTDL validation using Microsoft.Azure.DigitalTwins.Parser
• A sample model (Pizza.ttl) and its converted DTDL model (Pizza.json)
• Simple, extensible

Usage

RdfToDtdlConverter.exe --rdf-file Pizza.ttl --dtdl-file Pizza.json --dtmi-prefix com:example --model-version 2

Options

--rdf-file          Path to rdf input file. Example, c:\Pizza.ttl
--dtdl-file         DTDL output file. Example, Pizza.json
--dtmi-prefix       Digital Twin Model Identifier prefix. Example, com:example
--model-version     Digital Twin Model Identifier model version. Example, 1 as in dtmi:com:example:Thermostat;1

OWL/RDFS to DTDL Mapping

The RdfToDtdlConverter maps OWL/RDFS constructs to DTDL v2 constructs according to the following table:

RDFS/OWL Construct		DTDL Construct
Classes	owl:Class	Interface	@type:Interface
	IRI suffix		@id
	rdfs:label		displayName
	rdfs:comment		comment
Subclasses	owl:Class	Interface	@type:Interface
	IRI suffix		@id
	rdfs:label		displayName
	rdfs:comment		comment
	rdfs:subClassOf		extends
Datatype Properties	owl:DatatypeProperty	Interface Properties	@type:Property
	rdfs:label or INode		name
	rdfs:label		displayName
	rdfs:range		schema
	rdfs:comment		comment
Annotation Properties	owl:AnnotationProperty	Interface Properties	@type:Property
	rdfs:label or INode		name
	rdfs:label		displayName
	rdfs:range		schema
	rdfs:comment		comment
Object Properties	owl:ObjectProperty	Relationship	@type:Relationship
	rdfs:label or INode		name
	rdfs:range		target or omitted if no rdfs:range
	rdfs:comment		comment
	rdfs:label		displayName

Depending on the model, you may need to modify the code and mappings. For example, some industry models use skos:definition rather than rdfs:comment.

For DTDL Property, the following primitive schema mappings have been implemented:

_map.Add("http://www.w3.org/2001/XMLSchema#boolean", "boolean");
_map.Add("http://www.w3.org/2001/XMLSchema#date", "date");
_map.Add("http://www.w3.org/2001/XMLSchema#dateTime", "dateTime");
_map.Add("http://www.w3.org/2001/XMLSchema#double", "double");
_map.Add("http://www.w3.org/2001/XMLSchema#duration", "duration");
_map.Add("http://www.w3.org/2001/XMLSchema#float", "float");
_map.Add("http://www.w3.org/2001/XMLSchema#int", "integer");
_map.Add("http://www.w3.org/2001/XMLSchema#integer", "integer");
_map.Add("http://www.w3.org/2001/XMLSchema#long", "long");
_map.Add("http://www.w3.org/2001/XMLSchema#string", "string");
_map.Add("http://www.w3.org/2001/XMLSchema#time", "time");

Other Implementation Details

• By default, all DTDL properties have their writable property set to true
• owl:Restriction -> DTDL not implemented.
• owl:? -> DTDL Telemetry not implemented.
• owl:? -> DTDL Command not implemented.
• owl:? -> DTDL Component not implemented.
• owl:Imports are not imported. The DTDL parser will flag these missing Interfaces during the validation phase with the following message:
  • No DtmiResolver provided to resolve requisite reference(s): dtmi:...
  • You can add these Interfaces manually to the JSON output file.
• owl:DisjointWith we assume all owl:Classes are disjoint, even if owl:disjointWith is omitted.
  • In DTDL v2, a twin instance can only be created from a single DTDL interface.
  • As a work around, you can use TDL’s extends property to create another Interface that inherits from two other DTDL Interfaces, and create your twin instance from it.
• owl:ObjectProperty + owl:Domain + owl:Range are required to create a DTDL Relationship.
  • If no owl:Range, we omit target, which means the target can be any interface.
  • If no owl:Domain, the DTDL relationship is not created.