The OPC UA Standards include provisions for auditing. Auditing is an important security and tracking concept. Audit records provide the “Who”, “When” and “What” information regarding user interactions with a system. These audit records are especially important when Alarm management is considered. Alarms are the typical instrument for providing information to a user that something needs the user’s attention. A record of how the user reacts to this information is required in many cases. Audit records are generated for all Method calls that affect the state of the system, for example, an Acknowledge Method call would generate an AuditConditionAcknowledgeEventType Event.
The standard AuditEventTypes defined in OPC 10000-5 already include the fields required for Condition related audit records. To allow for filtering and grouping, this standard defines a number of sub-types of the AuditEventTypes but without adding new fields to them.
This standard describes the AuditEventType that each Method is required to generate. For example, the Disable Method has an AlwaysGeneratesEvent Reference to an AuditConditionEnableEventType. An Event of this type shall be generated for every invocation of the Method. The audit Event describes the user interaction with the system, in some cases this interaction may affect more than one Condition or be related to more than one state.