Dictionary References allow to reference externally defined Dictionaries like ECLASS or the Common Data Dictionary of the IEC to bind an OPC UA Node to the semantic defined in that dictionary. OPC 10000-19 defines the OPC UA mechanism for this. This includes, that the NodeIds of the Dictionary Entries use a specific NodeId in a specific Namespace, one Namespace for IRDIs and one for URIs.

In theory, the Server does not need to provide the Nodes of those NodeIds, but Clients would look up the dictionaries or already have internal knowledge about those dictionaries.