Event Areas in the A&E COM Server are represented in the A&E COM UA Wrapper as Objects with a TypeDefinition of BaseObjectType. The EventNotifier Attribute for these Objects always has the SubscribeToEvents flag set to True.

The root Area is represented by an Object with a BrowseName that depends on the UA Server. It is always the target of a HasNotifier Reference from the Server Node. The root Area allows multiple A&E COM Servers to be wrapped within a single UA Server.

The Area hierarchy is discovered with the BrowseOPCAreas and the GetQualifiedAreaName Methods. The Area name returned by BrowseOPCAreas is used as the BrowseName and DisplayName for each Area Node. The QualifiedAreaName is used to construct the NodeId. The NamespaceURI qualifying the NodeId and BrowseName is a unique URI assigned to the combination of machine and COM Server.

Each Area is the target of HasNotifier Reference from its parent Area. It may be the source of one or more HasNotifier References to its child Areas. It may also be a source of a HasEventSource Reference to any sources in the Area.

The A&E COM Server may not support filtering by Areas. If this is the case then no Area Nodes are shown in the UA Server address space. Some implementations could use the AREAS Attribute to provide filtering by Areas within the A&E COM UA Wrapper.

Event Sources in the A&E COM Server are represented in the A&E COM UA Wrapper as Objects with a TypeDefinition of BaseObjectType. If the A&E COM Server supports source filtering then the SubscribeToEvents flag is True and the Source is a target of a HasNotifier Reference. If source filtering is not supported the SubscribeToEvents flag is False and the Source is a target of a HasEventSource Reference.

The Sources are discovered by calling BrowseOPCAreas and the GetQualifiedSourceName Methods. The Source name returned by BrowseOPCAreas is used as the BrowseName and DisplayName. The QualifiedSourceName is used to construct the NodeId. Event Source Nodes are always targets of a HasEventSource Reference from an Area.

Event Categories in the A&E COM Server are represented in the UA Server as ObjectTypes which are subtypes of BaseEventType. The BrowseName and DisplayName of the ObjectType Node for Simple and Tracking Event Types are constructed by appending the text ‘EventType’ to the Description of the Event Category. For Condition Event Types the text ‘AlarmType’ is appended to the Condition Name.

These ObjectType Nodes have a super type which depends on the A&E Event Type, the Event Category Description and the Condition Name; however, the best mapping requires knowledge of the semantics associated with the Event Categories and Condition Names. If an A&E COM UA Wrapper does not know these semantics then Simple Event Types are subtypes of BaseEventType, Tracking Event Types are subtypes of AuditEventType and Condition Event Types are subtypes of the AlarmType. Table D.1 defines mappings for a set of “well known” Category description and Condition Names to a standard super type.

Table D.1 – Mapping from standard Event categories to OPC UA Event types

COM A&E Event Type	Category Description	Condition Name	OPC UA EventType
Simple	---	---	BaseEventType
Simple	Device Failure	---	DeviceFailureEventType
Simple	System Message	---	SystemEventType
Tracking	---	---	AuditEventType
Condition	---	---	AlarmType
Condition	Level	---	LimitAlarmType
Condition	Level	PVLEVEL	ExclusiveLevelAlarmType
Condition	Level	SPLEVEL	ExclusiveLevelAlarmType
Condition	Level	HI HI	NonExclusiveLevelAlarmType
Condition	Level	HI	NonExclusiveLevelAlarmType
Condition	Level	LO	NonExclusiveLevelAlarmType
Condition	Level	LO LO	NonExclusiveLevelAlarmType
Condition	Deviation	---	NonExclusiveDeviationAlarmType
Condition	Discrete	---	DiscreteAlarmType
Condition	Discrete	CFN	OffNormalAlarmType
Condition	Discrete	TRIP	TripAlarmType

There is no generic mapping defined for A&E COM sub-Conditions. If an Event Category is mapped to a LimitAlarmType then the sub Condition name in the Event are be used to set the state of a suitable State Variable. For example, if the sub-Condition name is “HI HI” then that means the HighHigh state for the LimitAlarmType is active

For Condition Event Types the Event Category is also used to define subtypes of BaseConditionClassType.

Figure D.1 illustrates how ObjectType Nodes created from the Event Categories and Condition Names are placed in the standard OPC UA HasNotifier hierarchy.

Figure D.1 – The type model of a wrapped COM AE server

Event Attributes in the A&E COM Server are represented in the UA Server as Variables which are targets of HasProperty References from the ObjectTypes which represent the Event Categories. The BrowseName and DisplayName are the description for the Event Attribute. The data type of the Event Attribute is used to set DataType and ValueRank. The NodeId is constructed from the EventCategoryId, ConditionName and the AttributeId.

The A&E COM UA Wrapper creates a Subscription with the COM AE Server the first time a MonitoredItem is created for the Server Object or one of the Nodes representing Areas. The Area filter is set based on the Node being monitored. No other filters are specified.

If all MonitoredItems for an Area are disabled then the Subscription will be deactivated.

The Subscription is deleted when the last MonitoredItem for the Node is deleted.

When filtering by Area the A&E COM UA Wrapper needs to add two Area filters: one based on the QualifiedAreaName which forms the NodeId and one with the text ‘/*’ appended to it. This ensures that Events from sub areas are correctly reported by the COM AE Server.

A simple A&E COM UA Wrapper will always request all Attributes for all Event Categories when creating the Subscription. A more sophisticated wrapper may look at the EventFilter to determine which Attributes are actually used and only request those.

Table D.2 lists how the fields in the ONEVENTSTRUCT that are used by the A&E COM UA Wrapper are mapped to UA BaseEventType Variables.

Table D.2 – Mapping from ONEVENTSTRUCT fields to UA BaseEventType Variables

UA Event Variable	ONEVENTSTRUCT Field	Notes
EventId	szSource szConditionName ftTime ftActiveTime dwCookie	A ByteString constructed by appending the fields together.
EventType	dwEventType dwEventCategory szConditionName	The NodeId for the corresponding ObjectType Node. The szConditionName maybe omitted by some implementations.
SourceNode	szSource	The NodeId of the corresponding Source Object Node.
SourceName	szSource	-
Time	ftTime	-
ReceiveTime	-	Set when the Notification is received by the wrapper.
LocalTime	-	Set based on the clock of the machine running the wrapper.
Message	szMessage	Locale is the default locale for the COM AE Server.
Severity	dwSeverity	-

Table D.3 lists how the fields in the ONEVENTSTRUCT that are used by the A&E COM UA Wrapper are mapped to UA AuditEventType Variables.

Table D.3 – Mapping from ONEVENTSTRUCT fields to UA AuditEventType Variables

UA Event Variable	ONEVENTSTRUCT Field	Notes
ActionTimeStamp	ftTime	Only set for tracking Events.
Status	-	Always set to True.
ServerId	-	Set to the COM AE Server NamespaceURI
ClientAuditEntryId	-	Not set.
ClientUserId	szActorID	-

Table D.4 lists how the fields in the ONEVENTSTRUCT that are used by the A&E COM UA Wrapper are mapped to UA AlarmType Variables.

Table D.4 – Mapping from ONEVENTSTRUCT fields to UA AlarmType Variables

UA Event Variable	ONEVENTSTRUCT Field	Notes
ConditionClassId	dwEventType	Set to the NodeId of the ConditionClassType for the Event Category of a Condition Event Type. Set to the NodeId of BaseConditionClassType Node for non-Condition Event Types.
ConditionClassName	dwEventType	Set to the BrowseName of the ConditionClassType for the Event Category of Condition Event Type. To set “BaseConditionClass" non-Condition Event Types.
ConditionName	szConditionName	-
BranchId	-	Always set to NULL.
Retain	wNewState	Set to True if the OPC_CONDITION_ACKED bit is not set or OPC_CONDITION_ACTIVE bit is set.
EnabledState	wNewState	Set to "Enabled" or "Disabled"
EnabledState.Id	wNewState	Set to True if OPC_CONDITION_ENABLED is set
EnabledState. EffectiveDisplayName	wNewState	A string constructed from the bits in the wNewState flag. The following rules are applied in order to select the string: "Disabled" if OPC_CONDITION_ENABLED is not set. "Unacknowledged" if OPC_CONDITION_ACKED is not set. "Active" if OPC_CONDITION_ACKED is set. "Enabled" if OPC_CONDITION_ENABLED is set.
Quality	wQuality	The COM DA Quality converted to a UA StatusCode.
Severity	dwSeverity	Set based on the last Event received for the Condition instance. Set to the current value if the last Event is not available.
Comment	-	The value of the ACK_COMMENT Attribute
ClientUserId	szActorID	-
AckedState	wNewState	Set to "Acknowledged" or "Unacknowledged "
AckedState.Id	wNewState	Set to True if OPC_CONDITION_ACKED is set
ActiveState	wNewState	Set to "Active" or "Inactive"
ActiveState.Id	wNewState	Set to True if OPC_CONDITION_ACTIVE is set
ActiveState.TransitionTime	ftActiveTime	This time is set when the ActiveState transitions from False to True. Note: Additional logic applies to exclusive limit alarms, in that the LimitState.TransitionTime also needs to be set, but this is set each time a limit is crossed (multiple limits might exist). For the initial transition to True the ftActiveTime is used for both LimitState.TransitionTime and ActiveState.TransitionTime. For subsequent transition the ActiveState.Transition time does not change, but the LimitState.TransitionTime will be updated with the new ftActiveTime. For example, if an alarm has Hi and HiHi limits, when the Hi limit is crossed and the alarm goes active the ftActiveTime is used for both times, but when the HiHi limit is later crossed, the ftActiveTime is only be used for the LimitState.TransitionTime. Note: The ftActiveTime is part of the key for identifying the unique event in the A&E server and needs to be saved for processing any commands back to the A&E Server.

The A & C Condition Model defines other optional Variables which are not needed in the A&E COM UA Wrapper. Any additional fields associated with Event Attributes are also reported.

Condition instances do not appear in the UA Server address space. Conditions can be acknowledged by passing the EventId to the Acknowledge Method defined on the AcknowledgeableConditionType.

Conditions cannot be enabled or disabled via the COM A&E Wrapper.

The COM A&E Wrapper does not store the state of Conditions. When ConditionRefresh is called the Refresh Method is called on all COM AE Subscriptions associated with the ConditionRefresh call. The wrapper needs to wait until it receives the call back with the bLastRefresh flag set to True in the OnEvent call before it can tell the UA Client that the Refresh has completed.