Many Historians will collection information from internal nodes or from some underlying system. The collected information might be obtained using non-OPC UA communication. This type of historical configuration is vendor specific.

Some Historians might collected information from other OPC UA Servers. The Historian might mirror the point in their own information models and use the HasCurrentData or the HasCurrentEvent Reference to indicate the source node for the data or Event. Mirroring Variables is typically simple. Variables usually do not have complex structure or nested Variables under them. For Events, the source of Events might be the Server Node or some higher level Object and replicating that Object or entire Server and the complex structure under it would not make sense.

Instance of this ObjectType are used in a Historian to indicate the historical collection related details of an event stream that is being sourced from another OPC UA Server. An instance of this ObjectType shall include a HasCurrentEvent reference to the remote Server Object that is the source of the Events that are being collected.

Table 12 – HistoricalExternalEventSourceType definition

Attribute	Value
BrowseName	HistoricalExternalEventSourceType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
HasProperty	Variable	Server	String	PropertyType	Optional
HasProperty	Variable	EndpointUrl	String	PropertyType	Optional
HasProperty	Variable	SecurityMode	MessageSecurityMode	PropertyType	Optional
HasProperty	Variable	SecurityPolicyUri	String	PropertyType	Optional
HasProperty	Variable	IdentityTokenPolicy	UserTokenPolicy	PropertyType	Optional
HasProperty	Variable	TransportProfileUri	String	PropertyType	Optional
HasProperty	Variable	HistoricalEventFilter	EventFilter	PropertyType	Mandatory
ConformanceUnits
Historical Access External Event Source

All instances of HistoricalExternalEventSourceType shall set the Object Attributes bits as described in 5.4.4.

An instance of this ObjectType may also have a HasHistoricalConfiguration to an instance of HistoricalEventConfigurationType, if it does not then the Server level default configuration shall apply.

The following optional information can be provided to describe how the Historian connects to receive the event stream:

• Server is a URI that represents a logical name for a Server that is the source of the event stream (see OPC 10000-4 ServerUri for additional details).
• EndpointUrl is a String that provides the URL for the Endpoint used for the connection.
• SecurityMode is a MessageSecurityMode enumeration that describes the type of security to apply to the messages in this connection.
• SecurityPolicyUri a string that describes the URI for SecurityPolicy used when securing messages for this connection.
• IdentityTokenPolicy is the type of UserIdentity token that is used for this connection.
• TransportProfileUri is a string that describes the URI of the transport profile use for this connection.

HistoricalEventFilter is mandatory and is defined in 5.4.2