The namespace is a URI that identifies the naming authority responsible for assigning the identifier element of the NodeId. Naming authorities include the local Server, the underlying system, standards bodies and consortia. It is expected that most Nodes will use the URI of the Server or of the underlying system.
Using a namespace URI allows multiple OPC UA Servers attached to the same underlying system to use the same identifier to identify the same Object. This enables Clients that connect to those Servers to recognise Objects that they have in common.
Namespace URIs, like Server names, are identified by numeric values in OPC UA Services to permit more efficient transfer and processing (e.g. table lookups). The numeric values used to identify namespaces correspond to the index into the NamespaceArray. The NamespaceArray is a Variable that is part of the Server Object in the AddressSpace (see OPC 10000-5 for its definition).
The URI for the OPC UA namespace is:
Its corresponding index in the namespace table is 0.
The namespace URI is case sensitive.