As illustrated in the figure below, the A&E COM UA Proxy is a COM Servercombined with a UA Client. It maps the Alarmsand Conditionsaddress space of UA A&C Serverinto the appropriate COM Alarms and Event Objects.
Subclauses D.3.2through D.3.9identify the design guidelines and constraints used to develop the A&E COM UA Proxy provided by the OPC Foundation. In order to maintain a high degree of consistency and interoperability, it is strongly recommended that vendors, who choose to implement their own version of the A&E COM UA Proxy, follow these same guidelines and constraints.
The A&E COM Clientsimply needs to address how to connect to the UA A&C Server. Connectivity approaches include the one where A&E COM Clients connect to a UA A&C Serverwith a CLSID just as if the target Serverwere an A&E COM Server. However, the CLSID can be considered virtual since it is defined to connect to intermediary components that ultimately connect to the UA A&C Server. Using this approach, the A&E COM Clientcalls co-create instance with a virtual CLSID as described above. This connects to the A&E COM UA Proxy components. The A&E COM UA Proxy then establishes a secure channel and session with the UA A&C Server. As a result, the A&E COM Clientgets a COM Event Serverinterface pointer.