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Fetching the events from an OPC UA Server

CHIRANTAN JOSHI

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07/01/2024 - 06:34

Hi Team,

Our OPC UA client uses OPCUA legacy Java stack. The client retrieves the information model from the OPC UA server and then browses over it for listing the events to render on the UI. The following steps are being taken for this browsing process.
1. Check the selected node, if it subscribes to events add it to the list of events else find its children.
2. Iterate over the children. If the child is subtype of Identifiers.GeneratesEvent recursively call this function.
3. else go to the list of parents and find parents which are subtype of Identifiers.HasSubtype.
4. Iterate over these parents and recursively call this function.

While doing this below events are missed/filtered out and hence not rendered on the UI
1. SystemEventType
2. EventQueueOverflowEventType
3. TransitionEventType
4. SampleEventType
5. TraceEventType

Please assist to efficiently browse the information model so that all events can be listed and rendered for further mapping and deployment.

Thanks,

Chirantan

Randy Armstrong

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07/02/2024 - 16:07

The GeneratesEvent reference will not always be present.

Many events are only produced by the Server Object.

The events propagate up the HasNotifier references to the Server Object. If you want all events produced by a server you only subscribe to the Server Object. You subscribe to Objects lower in the HasNotifier hierarchy only when you want to restrict the events reported.

So it is not clear why you need any recursive operations.

CHIRANTAN JOSHI

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07/16/2024 - 23:22

Hi Randy,

Thanks for your reply. We need few more input to understand the issue with our client.

We noticed that when we drag and drop “Server” node in event view of UAExpert or Prosys Browser, it creates subscription on the server. This is not the case for our client.

On click event to the “Server” node on our client, it makes Browse and Read request to the server and pull the children and when we map it with client item, it displays the events of certain type only and certain other types of events are missed which we discussed above.

Is the subscription call required here to get all types of events?

Thanks,

Chirantan

Randy Armstrong

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07/22/2024 - 18:04

Yes, you need to create a subscription to receive events.

The subscription specifies what fields you receive and any filters to use.