UaExpert seems not to handle namspace array changes correctly

[kurt]

Hi support team,

we are creating several nodes managers dynamically, dependent on the availability of the corresponding underlying "data providers". Each gets its own namespace. Due to the nature of our underlying system we can not assume or expect a strict startup order, even one or more data providers might have been fallen away or new ones could have been added between two server runs. The only thing which can be guaranted ist the namespace name (URI), since this is directly mapped to the unique name of the underlying data provider.

According to my observations UaExpert seems not to handle changes in our UA servers namespace array correctly. Although according to the Book "OPC Unified Architecture" it should.

There are 2 situations:

- after a reconnect of UaExpert when the server has been restarted
- when opening a saved project after a server restart

In both cases UaExpert seems not to respect the (changed) namespace index at all, but only looking for the numerical index (which has changed in between). In fact UaExpert can get notifications from the wrong data provider. Since the node ids might be identical except for the namespace index.

- Is this a known limitation, bug or feature in UaExpert?

- Is my understanding of the expected behaviour correct (clients should only rely on the namespace name after a server restart or reconnect)?

- What can we expect from an "average" UA client implementation?

- Even if our implementation is correct according to spec, is it wise to work with dynamic namespace arrays in this way at all?

- Is it possible to share the same namespace name (URI) between several node managers? What would be the downside.

Looking forward to your answers.

Best regards
Kurt

[Support Team]

Hello,

- Is this a known limitation, bug or feature in UaExpert?

This is a known issue in UaExpert and will get fixed in the next version.

- Is my understanding of the expected behaviour correct (clients should only rely on the namespace name after a server restart or reconnect)?

Your understanding of the expected behaviour is correct. A client should remember the namespace table and map the namespace indices of NodeIds accordingly on reconnect.

- What can we expect from an "average" UA client implementation?

Every UA client should be aware of the fact that the namespace table might change after a server restart. On the other hand, there might always be clients that don't react on namespace table changes.

- Even if our implementation is correct according to spec, is it wise to work with dynamic namespace arrays in this way at all?

This depends on your requirements and the underlying systems. For identifying nodes of an underlying system, using namespace URIs is the easiest way and also intended like this by UA. Another approach would be to add information about the underlying system into the NodeId identifier, but that might lead to complicated NodeIds.

- Is it possible to share the same namespace name (URI) between several node managers? What would be the downside.

If you're using our C++-SDK this is not possible out of the box. You would have to register a node manager for the namespace URI and then create one additional node manager for each underlying system. Then, from the 'main' node manager you could distribute the requests to the responsible 'underlying' node managers.

[Support Team]

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