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Namespace uri used in ReferenceDescription.nodeId for browsing
November 14, 2017
16:36, EET
Forum Posts: 4
Member Since:
November 14, 2017
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I’ve encountered the Simulation Server filling in namespace uris as for the ReferenceDescription.nodeId in the returned ReferenceDescriptions when browsing the address space. I’ve never seen an OPC UA server doing this before and I just want to ask about what the best way would be for returning the references here.
In the standard, we have this:
“If the serverIndex indicates that the TargetNode is a remote Node, then the nodeId shall contain the absolute namespace URI. If the TargetNode is a local Node the nodeId shall contain the namespace index.”
Since the nodes of the Simulation Server are of “local” type, I did not expect to get the namespace URI here…

thanks for help or clarification

November 14, 2017
17:57, EET
Bjarne Boström
Forum Posts: 860
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April 3, 2012
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This is a known “issue” in the java stack (https://github.com/OPCFoundation/UA-Java/issues/12), which is a low level component, on top of which our java SDK is built, which is in turn used to make the SimulationServer.

You are correct about the specification stating that. This will be eventually fixed, however the fix is more of a performance optimization than a real issue, in my opinion.

However in practice a client should not rely on the namespace uri defining a remote reference, because the serverIndex defines that, not the uri. Therefore it should always check the server index first to determine if the reference is local/remote, then check namespaceuri/index, convert the index to uri if index defined and then check the value.

In general, the namespace indices should not be used for anything other that efficient transmit of the uri, i.e. clients should always convert the indices to uris and code application logic against the uris instead of indices, unless their developer maintains all client accessing that server because the order of the indices is not defined (expect for the 0 and 1 namespace indices) and could e.g. different each restart.

– Bjarne

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