Nodesare unambiguously identified using a constructed identifier called the NodeId. Some Serversmay accept alternative NodeIdsin addition to the canonical NodeIdrepresented in this Attribute. A Servershall persist the identifierType and identifier NodeId elementsof a Node as well as the Namespace Uri which the namespaceIndex NodeId element references.A Servermay change the namespaceIndex NodeIdelement of a Node with future Sessionsand therefore a Clientshall not assume the namespaceIndexwill not change. The structure of the NodeIdis defined in 8.2.