The system architecture as shown in Figure 6 has already been defined in FDT2 specification.
The OPC UA server is a Frame Application. The Frame Application is interacting with the DTMs in order to manage the device-specific information and in order to interact with the devices. Frame Applications may support different use cases, for example: vendor-specific service, process control or asset management. Frame Applications may start and terminate the DTMs on demand (e.g. only if a value is read from the respective device).
The OPC UA server is equipped with an OPC UA server interface. In the information model of the OPC UA server the application-specific project information may be represented (depending on the Frame Application) and device-specific information shall be represented. The OPC UA client may browse the information model and may use the services of the OPC UA interface to access the represented information. If device-specific information is accessed, the information is retrieved from the DTMs.
In a multi-client scenario the Frame Application is responsible for managing the access to the DTMs. The approach for managing the access from multiple clients is to use the "multi user access" as specified in FDT2 specification.
Figure 6 – System architecture according to FDT2 Specification
Since the contents of the FDT project and the management of multi-client access is specific to the Frame Application, this document focuses on the mapping of the information from the DTM to the ‘Device model’ of OPC UA for Devices. One possible approach for presentation of the project information would be the 'Device Integration Host Model' according to OPC UA for Devices.