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As cities continue connecting their urban environments, the concept of digital twins—a digital representation of real-world environments brought to life with real time data from sensors and other data sources—has entered the realm of smart cities and promises to enable city administrations and urban planners to make better decisions with the help of data integration and visualization from across the urban space. 


Last year, we announced the general availability of the Azure Digital Twins platform which enables developers to model and create digital representations of connected environments like buildings, factories, farms, energy networks, railways, stadiums, and cities, then bring these entities to life with a live execution environment that integrates IoT and other data sources.


Today, we are excited to announce that the open-source GitHub repository of Smart Cities ontology for Azure Digital Twins available to the ecosystem.


Why ontologies


To drive openness and interoperability, Azure Digital Twins comes with an open modeling language, Digital Twins Definition Language (DTDL), which provides flexibility, ease of use, and integration into the rest of the Azure platform. Using DTDL, developers can describe twins in terms of the telemetry they emit, the properties they report or synchronize and the commands they respond to. Most importantly, DTDL also allows describing the relationship between twins.


Common representation of places, infrastructure, and assets will be paramount for interoperability and enabling data sharing between multiple domains. It’s our goal to partner with industry experts and provide DTDL-based ontologies which learn from, build on, and/or use industry standards, meet the needs of developers, and are adopted by the industry. The resulting open-source ontologies provide common ground for modeling connected environments, accelerate developers’ time to results, and enable interoperability between DTDL-based solutions from different solution providers.


Smart Cities ontology approach and overview


We collaborated with Open Agile Smart Cities (OASC) and Sirus to provide a DTDL-based ontology, starting with ETSI CIM NGSI-LD, and  accelerate development of digital twins-based solutions for smart cities.


In addition to ETSI NGSI-LD, we’ve also evaluated Saref4City, CityGML, ISO and others. 


The ETSI CIM NGSI-LD specification defines an open framework for context information exchange named NGSI-LD which comes with an information model that defines the meaning of the most needed terms, and a domain-specific extension to model any information. The core meta-model provides a basis for representing property graphs using RDF/RDFS/OWL, and is formed of Entities, their Relationships, and their Properties with values, encoded in JSON-LD. In addition to the core meta-model, NGSI-LD compliant open models for aspects of smart cities have been defined by organizations and projects, including OASC, FIWARE, GSMA and the Synchronicity project. The NGSI-LD models for Smart Cites comprise models in the domains of Mobility, Environment, Waste, Parking, Building, Park, Port, etc.


The property graph nature of NGSI-LD made it quite straightforward to map it to DTDL, and with today’s release, we are making an initial set of DTDL models adapted from the NGSI-LD open models for Smart Cities available to the community.

We’ve focused our initial set on use cases that are increasingly relevant to cities given the availability of IoT devices and sensors, like measuring the air quality in a neighborhood, understanding the noise level in a district, the crowd flow in a road segment, traffic flow in a road segment, monitoring on-street parking in parking spots, availability of EV-Charging, or monitoring streetlights and reducing energy consumption, but as well enabling streetlight infrastructure for additional smart cities services enabling citizen-centric use cases.




In addition to the ETSI NGSI-LD, we’ve also started leveraging ETSI SAREF extension for Smart Cities ontology framework for Topology, Administrative Area and City Object modeling. Using Saref4City ontology constructs represented in DTDL allowed us to model city objects like poles, their containment within an administrative area of a city, and linked to the smart models in the domain of mobility, environmental, parking adapted in DTDL from NGSI-LD models for Smart Cities described above.


Watch this IoT Show episode to learn how we approached the DTDL-based Smart Cities ontology, how we mapped the ETSI NGSI-LD models to DTDL, extending the ontology based on Saref4City, while bringing it all together with an example use case brought to life with Azure Digital Twins Explorer.




We collaborated with OASC and Sirus to bring the first DTDL ontology for Smart Cities for Azure Digital Twins to the community. We are also working with more partners that are validating and contributing to the open source ontology.


Open & Agile Smart Cities – OASC in short –is an international network of cities and communities, working with local public administrations of all sizes to support their digital transformation journey. Together with its members, partners, and experts, OASC creates sustainable impact for cities with data driven solutions based on a Minimal Interoperability Mechanisms which includes open standards, open APIs, and a recommended catalog of open data models, including NGSI-LD models, to enable interoperability for applications and systems among different cities. 


Sirus is a dynamic software integration company that specializes in building IoT and Smart City solutions. Sirus enables cities to build digital solutions and integrate data from a variety of IoT devices and other systems through an open standards-based approach, like ETSI NGSI-LD, and has pioneered multiple smart cities data integration platforms including for the City of Antwerp. Sirus invests heavily in innovation, like smart city digital twins based on Azure and pioneers in open standards implementations. Sirus is also an SME partner of OASC. 


Siemens MindSphere City Graph is a solution that offers a new way to optimize city operations. It creates a digital twin of urban spaces allowing cities to model, monitor, and control physical infrastructure, powered by Azure Digital Twins. MindSphere City Graph uses the Digital Twins Definition Language and context information management specifications ETSI NGSI-LD to drive openness for solution providers to integrate and deliver sustainable value for a city while enabling open data for cities through open standard approach. The open source DTDL-based ontologies for Smart Cities based on ETSI NGSI-LD will accelerate the development of digital twins solutions and integration.


ENE.HUB, a portfolio of Brookfield Infrastructure Partners, is a fully integrated smart city infrastructure as a service provider. ENE.HUB’s flagship product, the SMART.NODE™ is a comprehensive and self-contained smart pole solution that integrates a range of smart city services including smart lighting, communication services, energy services, environment services, transport services, safety, and media services. ENE.HUB is collaborating with Microsoft on digital twin’s representation of smart poles based on the open DTDL-based Smart Cities ontology.


We also continue to collaborate with our partners Bentley Systems and Imec, experts in digital twin solutions for smart cities. Both Bentley Systems and Imec are also members of the Digital Twin Consortium along with Microsoft.


Next steps


With this release of smart cities ontology for digital twins, we’ve focused on an initial set of models and we welcome you to contribute to extend the initial set of use cases, as well as improve the existing models.


Explore the open-source GitHub repository, try it out with Azure Digital Twins, and learn how to contribute.


Our goal is to accelerate your development of digital twins solutions for smart cities and enable interoperability and data sharing for cities.


If you are interested in Smart Building solutions, we worked with the RealEstateCore consortium to provide DTDL based ontology for Smart Buildings. Similarly, we are also working on Energy Grid ontology which will be coming soon.


As part of our commitment to openness and interoperability, we also continue to promote best practices and shared digital twin models and use cases through the Digital Twin Consortium.


Brought to you by Dr. Ware, Microsoft Office 365 Silver Partner, Charleston SC.