Figure 5illustrates the simple case of a Clientcommunicating with a Server.

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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 Serverreceives the request and creates its own audit log entry for it. This entry is identified by its own audit id and contains its own Auditinginformation. It also includes the name of the Clientthat issued the service request and the Clientaudit entry id received in the request.

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