Digital Twin – Modeling Interrelated Devices
Standards such as OPC UA (OPC Connect) 2 , SensorML 3 , SSW (Semantic Sensor Web ) 4 , Sensor
Grid 5 , etc., were utilized, along with semantic information to capture the relationships between
these devices on the plant floor. This is similar to the above example but much more complex –
factories have thousands of data points with many hierarchical relationships between devices.
OPC UA’s Information Modeling 6 capability is the closest standard that meets the requirement
to model devices and their relationships and should be leveraged to generate the Semantic
Ontology for the Digital Twin representation of Smart Connected Factories or Connected Devices.
In OPC UA, objects and relationships are represented as shown in Figure 7.
Figure 7 OPC UA representation of an object
This follows an Object Oriented approach: Objects can be composed of objects and properties;
objects belong to types and you model the relationships between them.
Figure 8 shows an example of a temperature controller represented as Device Object. The
component ParameterSet contains all Variables describing the Device. The component Method
Set contains all Methods provide by the Device. Both components are inherited from the
TopologyElementType which is the root Object type of the Device Object type hierarchy. Objects
2 http://opcconnect.opcfoundation.org/2015/12/why-semantics-matter/
3 http://www.sensorml.com/sensorML-2.0/examples/helloWorld.html
4 https://en.wikipedia.org/wiki/Semantic_Sensor_Web
5 https://en.wikipedia.org/wiki/Sensor_grid
6 OPC UA Information Model https://opcfoundation.org/developer-tools/specifications-unified-architecture/part-5-information-model/
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March 2018