What is namespace in OPC-UA?

Question

I am novice to OPC Unified Architecture world and I'm studying it from basics. What exactly are namespaces and why it is always appended with NodeID?

Answer 1

A namespace in OPC UA is like a container for node ids. There is the predefined namespace with index 0 from the OPC foundation. And there are many more namespaces, e.g. DI, PLCopen. Each namespace belongs to a specific OPC UA specification, and every OPC UA specification can define its own node ids. To make sure a specific ID uniquely identifies a specific node within a namespace you need to indicate the namespace ID.

More information can be found in the official OPC UA specification:

https://reference.opcfoundation.org/v104/Core/docs/Part3/8.2.2/