Figure 5 illustrates the simple case of a Client communicating with a Server.


Figure 5 – Simple Servers

In this case, OPC Client “A” executes some auditable operation that includes the invocation of an OPC UA service in Server “D”. It writes its own audit log entry, and includes the identifier of that entry in the service request that it submits to the Server.

The Server receives the request and creates its own audit log entry for it. This entry is identified by its own audit id and contains its own Auditing information. It also includes the name of the Client that issued the service request and the Client audit entry id received in the request.

Using this information, an auditor can inspect the collection of log entries of the Server and relate them back to their associated Client entries.