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the namespace alias table

The Namespace Alias Table is a crucial component in the OPC UA Address Space, allowing for efficient referencing of namespaces.

It provides a mapping between namespace indices and their corresponding URIs, also enabling the use of shorter identifiers to identity namespaces.

The short namespace alias is particularly convenient when you are interacting with a OPCUA server that is under developments. In such circumstances, the namespace index may change frequently, and using a short alias allows you to avoid having to update your NodeId references every time the namespace index changes.

Namespace aliases are also convenient as a mnemonic to remember the namespace index of a given namespace. For instance it is easier to remember di for the Device Information namespace than ns=3.

Benefits of Namespace Aliases​

Namespace aliases are used to simplify the representation of NodeIds and BrowsePaths in OPC UA. They provide several benefits:

  • Aliased namespaced NodeIds:

    na=di;i=5001 is equivalent to nsu=http://opcofundation.org/UA/DI;i=5001 or ns=3;i=5001 (assuming that the Device Information namespace is at index 3).

  • Aliased BrowsePaths:

    /di:DeviceSet/dt1:MyDevice/dt1:Temperature is equivalent to /3:DeviceSet/1:MyDevice/1:Temperature (assuming that the Device Information namespace is at index 3, and the DT1 namespace is at index 1).

Namespace Alias Table​

The Namespace Alias table is avaiable in the third tab of the OPC UA Endpoint node configuration dialog.

The table provide a [Extract] button that you can use to extract the namespace aliases from the server's Namespace Array.

By default, standard namespace aliases are provided for common well known OPC UA namespaces, such as di for Device Information, machinery for Machinery , adi for Analyze Device Integration, autoId etc...`

Custom namespace aliases will be affected namespace in the form ns1, ns2, etc..

You can override these aliases by providing your own custom namespace aliases.

You can press the Extract button to extract the namespace aliases mutliple times. Even if the server namespace has been scrambled, the Extract button will always keep the current alias table intact, and will update the namespace index appropriately.