# Generic Digital Twin Architecture for Industrial Energy Systems
## 3 Proposed Generic Digital Twin Architecture
Thus, a combination of various protocols can be expected, which are made transparent to the upper layers by the Smart Data Service. Here, OPC Unified Architecture (OPC UA) is a representative in the context of Industry 4.0. Next to its communication capabilities, information modeling also enables the representation and access to context information through OPC UA. Information Layer--Within the Information Layer of the DT architecture, data is gathered and enriched with semantics and related with other context information. Thus, the data dimension of the 5D-DT becomes an information dimension at this stage. The central component inside the Information Layer is a Shared Knowledge base, which stores contextual information about resources and services. Data are linked with this information to add semantics to it. Different levels of semantic expressivity can be achieved by applying different information modeling technologies. Ideally, data are stored in their original formats in proper databases. The Shared Knowledge base acts as a semantic integration layer for run-time data and engineering data by providing access to historical data (archives) and holding contextual information inside the Shared Knowledge. Access to the information inside the Shared Knowledge is granted by an Information Query Service. This service can retrieve information from the knowledge base and provide it to other services. The Information Insertion Service is used to add or change information from the upper layers of the DT architecture inside the Shared Knowledge base. Thus, information ownership and access have to be managed including data access mechanisms. This is performed by an Information Management component inside the DT architecture, which handles the information access of the Query and Insertion Service. The above-mentioned components and services form the so-called Smart Data Service [23], which builds a central point of information inside the architecture. It provides information about resources and services through the Shared Knowledge base and makes it accessible for other services in the Functional Layer. Functional Layer--In the Functional Layer, the service dimension of the 5D-DT concept is realized. A service-oriented architecture is applied to enable loose coupling and cohesion of certain functionality [24]. The services of the DT can be grouped by their functionality and can build on each other. Five groups are identified: Simulation Services, Monitoring Services, Diagnosis Services, Prediction Services, Control Services, and Reconfiguration Services. Next to these functional services, a Service Management component takes care of service registration, discovery, and obtaining status information about certain services. This information about a service is part of the Shared Knowledge in the Information Layer and will be inserted and queried through the offered Smart Data Service interface. The resource management is not handled by a central component, as the services have to handle their resources by themselves, facilitating the Shared Knowledge base. Simulation Services are the core services, as they are part of the Virtual Entity of the 5D-DT concept. Typically, there exists not only one model of the physical entity in a DT, but a set of executable models that are specific for the intended purpose and also evolve over time [25]. Thus, different models for various domains, like the mechanical structure, thermal behavior, etc. can be hosted and used inside the Simulation Service of a DT. As for the other services, resources have to be managed by the service itself, and the related information about the models has to be made available through the Shared Knowledge base. A simulation model hosted by the Simulation Service in combination with related context information from the Shared Knowledge base generates a certain View of the Virtual Entity inside the DT. Monitoring Services are elementary services to acquire data from the physical entity and observe its current state.