The IdType element identifies the type of the NodeId, its format and its scope. Its values are defined in Table 23.
Table 23 – IdType Values
|GUID_2||Globally Unique Identifier|
|OPAQUE_3||Namespace specific format|
Normally the scope of NodeIds is the Server in which they are defined. For certain types of NodeIds, NodeIds can uniquely identify a Node within a system, or across systems (e.g. GUIDs). System-wide and globally-unique identifiers allow Clients to track Nodes, such as work orders, as they move between OPC UA Servers as they progress through the system.
Opaque identifiers are identifiers that are free-format byte strings that might or might not be human interpretable.
String identifiers are case sensitive. That is, Clients shall consider them case sensitive. Servers are allowed to provide alternative NodeIds (see 5.2.2) and using this mechanism severs can handle NodeIds as case insensitive.