Jouni Aro said

Yes, the namespaceIndex may change. So, if you store nodeIds on the client side, you should store the namespaceUri, instead of namespaceIndex. You can map between these, using the NamespaceTable of the server, available from UaClient.getNamespaceTable().

ExpandedNodeIds can use the namespaceUri instead of namespaceIndex. They also enable referring to nodes that point to a node on another server. Therefore some service methods in the UA interface are defined to use ExpandedNodeId instead of NodeId. That’s also why you see them both used in the BigNodeManager example as well.

Hi ,
I tried , but I am getting the same uri for all the node ids. For example if node id is ns=3;s=DataItem_0998 , index is 3 then I am getting the uri as http://www.prosysopc.com/OPCUA…..dressSpace . But we need an unique id . Can I accomplish this with uri concept ? Please suggest if I am doing anything wrong.

Thanks in advance.

Jouni Aro said

cto said

Hi ,
I tried , but I am getting the same uri for all the node ids. For example if node id is ns=3;s=DataItem_0998 , index is 3 then I am getting the uri as http://www.prosysopc.com/OPCUA…..dressSpace . But we need an unique id . Can I accomplish this with uri concept ? Please suggest if I am doing anything wrong.

Sorry, but I did not quite understand what you are trying.

The NodeId is composed of the Namespace and an ID. The namespace is usually defined with NamespaceIndex, e.g. 3, which refers to the index of the respective NamespaceUri in the NamespaceArray of the server. The index may change when the server is restarted, so it is not always safe to store NodeIds in the client using the indexes. Instead, you would store the NamespaceUri, e.g. http://www.prosysopc.com/OPCUA…..dressSpace.

The combination of the Namespace and the ID is always unique for the node.

Thanks got my answer . Now suppose I have the following output .

node id –>> ns=3;s=DataItem_0998 :: name space index —>> 3 :: name space uri —>> http://www.prosysopc.com/OPCUA…..dressSpace

In node id I get that node id = ns=3;s=DataItem_0998 where namespace index is 3 . My concern is that in the node id does the s=DataItem_0998 part is fixed ?

Jouni Aro said

Yes the ID-part is always fixed.

Is it possible that there in the same address space with different name space uri , tag with same id exists ? That is say I have DataItem_0998 against one uri and DataItem_0998 against another in the same address space ? Also is there any provision to know that the OPC UA server has restarted ? If the server restarts when I again connect is there any sdk method to know the node id with input namespace uri and id or I have to browse again and get it ?

Jouni Aro said

Yes, different name spaces may have the same IDs.

You can monitor the server status with UaClient.addServerStatusListener() to get notified of a server shutdown.

If you store the NamespaceUri and ID, you can use that later. You can use UaClient.getNamespaceTable() to convert the NamespaceUri to NamespaceIndex, which you need for NodeId.

Note that in normal circumstances, the namespaces of the server are not expected to change, but it is always possible.

Thanks. Could you please tell me how the namespace uri is constructed ? Suppose in the address space I have a tag located in the following location .

data–>dataitems–>dataitem1

So is the uri like data.dataitems.dataitem1.I guess it is not like that.

Jouni Aro said

No, there is no generic rule how the NodeID is constructed. You will need to find it out, by browsing or from the documentation of the server.

Thanks , is there a way that I can get the data type information of the tag ? Also another query is there a way so that I browse once and list all the tags in an address space in one go , instead of browsing individually ?

Jouni Aro said

cto said

Thanks , is there a way that I can get the data type information of the tag ?

You can read the DataType attribute. In the SDK, UaVariable.getDataType() and/or getDataTypeId().

Also another query is there a way so that I browse once and list all the tags in an address space in one go , instead of browsing individually ?

No there isn’t. Also when browsing you may get back to nodes that you have already browsed, so beware of infinite loops.

Hi,

Data was continuously getting fetched from OPC UA server , but suddenly the following exception is thrown. Could please explain this one .

02/02/2014 18:25:37.366 INFO [Blocking-Work-Executor-2279] org.opcfoundation.ua.transport.tcp.io.SecureChannelTcp – 318: Error recovery failed, security token has expired
02/02/2014 18:25:37.366 INFO [Blocking-Work-Executor-2279] org.opcfoundation.ua.transport.tcp.io.SecureChannelTcp – 318 Closed
02/02/2014 18:25:37.366 INFO [Blocking-Work-Executor-2279] org.opcfoundation.ua.transport.tcp.io.SecureChannelTcp – -1: Error recovery = false