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09/25/2016
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Hi,
If I have a simple nodes hierarchy like the Server “Organizes” a folder node (“folder_node”) and “folder_node” “Organizes” a variable node (“variable_node”). Further, “variable_node” is designed to the the source node of a condition node (“condition_node”). My questions are:
1. Should “folder_node” “Organizes” “condition_node”?
2. Does the event hierarchy have to be:
(1) “folder_node” “HasEventSource” of “variable_node”;
(2) “variable_node” “HasCondition” of “condition_node”;
3. As a supplement to the #2 question, is the event notifier of “condition_node” required to be “folder_node”? Can I and assign other event notifier to “condition_node”?
Many thanks,
-Hong
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02/24/2014
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Hong,
I’m not sure I understand your question, but it appears to be related to events and event hierarchies
so in the OPC UA model there are a number of ReferenceTypes that are related to events and creating a hierarchy of events sources.
HasEventSource => (Hierarchical reference) source of the reference is always an Object that a client can subscribe to to obtain events, The target is any node that can generate an event, which would be reported to the client that subscribed to events from the source node.
HasNotifier => subtype of HasEventSource, its source is the same as HasEventSource, but the Target can only be other Objects that can a client can also subscribe to to obtain events.
HasCondition => This reference (non-Hierarchical reference) is use to identify Conditions that are associated with Objects or variable (or ObjectType and VariableTypes). The source is always a node that is pointed to by a HasEventSource reference (Target of the HasEventSource reference). The Target of the HasConditionReference is always a ConditionType (or subtype of it) or an instance of a ConitionType (or subtypes of it)
The structure you would created with the first two reference is entirely up to you as long as the reference are used correctly, i.e. the folder could be an object that a client could subscribe to and obtain events from and it could reference items below it with either of the reference (depending on what you want to construct). The last reference can be used through out the structure to point to specific Conditions. Multiple nodes can point to the same condition (especially if it is a type).
It is also important to remember that some Servers will not create an event hierarchy, they will only report all events via the Server Node. Also Server may not provide HasCondition references from nodes to Conditions that they generate, or they might only provide some of the condition types that a node could generate (i.e. not a complete list).
Providing the event Hierarchy can be very helpful to clients and is recommended in may cases. The HasCondition reference is also very helpful to client, especially if a client is expect to provide specific behavior for certain conditions.
Paul
Paul Hunkar - DSInteroperability
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