QuickOPC User's Guide and Reference
Namespace indices in qualified names
Fundamentals > Identifying Information in OPC UA Client-Server > OPC UA Qualified Names > Namespace indices in qualified names

During most communication between the client and the server, OPC Unified Architecture uses namespace indices, which are integer numbers, to distinguish between namespaces. The namespaces indices reference a namespace table made available by the server, and only the namespace table actually contains the namespace URIs. The order of entries in the server’s namespace table can change between sessions. For this reason, namespace indices should not be persisted, as they alone are not generally sufficient to identify a namespace and thus a qualified name.

There are, however, situations where you may want to include the namespace index in the expanded qualified name string: 

For situations like this, QuickOPC-UA allows the use of “ns=…” notation for a namespace index inside the expanded qualified name strings, and has two additional provisions:

Note that namespace index 0 (zero) is reserved for the standard namespace maintained by the OPC Foundation ("http://opcfoundation.org/UA/"), and is not usually specified inside the expanded qualified name strings.

See Also

Examples - OPC Unified Architecture