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I have noticed that all OPC tag Ids are prefixed with ns=2;s=.
Some examples of possible NodeId values would be:
ns=2;s=AcquisitionTimeRemainingns=2;s=Statusns=2;s=TimeI am wondering what the significance of this prefix is.
Someone else asked this question on a forum. The answer given was that ns prefix specifies the namespace index a NodeId belongs to. The answer-er goes on to state:
For weird historical reasons, we assume ns=1 if it’s not explicitly present. Kepware’s Nodes are all in ns=2, so, it must be specified.
I am not using "Kepware's Nodes" and my namespace is still set to 2... Will this always be 2? I could not find any information on what the s in the prefix represents.
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Some Nodes are Variables, DataType, References, Object, Methods... depending of what they are used for. By reading the OPC UA Specification you will get a good overview here - Specially Part 1: Overview and Concepts and Part 3: Address Space Model (you need to create a free account first) NodeOPCUA, which is a Node.js implementation of OPC UA.
The answer-er goes on to state: For weird historical reasons, we assume ns=1 if it’s not explicitly present. Kepware’s Nodes are all in ns=2, so, it must be specified. I am not using "Kepware's Nodes" and my namespace is still set to 2... Will this always be 2? I could not find any information on what the s in the prefix represents.
I could not find any information on what the s in the prefix represents. ns=2 is indicating namespace index 2. s=foo is indicating it's a String type NodeId with value "foo". This syntax is borrowed from the syntax used to encode a NodeId in the OPC UA XML encoding:
What exactly are namespaces and why it is always appended with NodeID? YOu can consider namespace as a distinguisher Nodes from Different Sources, As a server can have nodes from multiple sources so namespaces are one which exposes which node belongs, under which tree. A namespace in OPC UA is like a container for node ids.
ns=2 is indicating namespace index 2.
s=foo is indicating it's a String type NodeId with value "foo".
There are 4 types of NodeId:
This syntax is borrowed from the syntax used to encode a NodeId in the OPC UA XML encoding:
ns=<namespaceindex>;<type>=<value>
What namespace nodes appear in and how many namespaces there are depends on the server you are connected to.
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The namespace values are only depending of your OPC UA Server and its configuration. What is mandatory is that 0 is reserved for OPC UA default namespace.
You can read/subscribe to the OPC UA Node which value describe your OPC UA Server Namespace configuration at "ns=0;i=2255" (Server_NamespaceArray). The Node value is an array of all the Namespace available at this Server
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