Clause 5 defines the NodeClassesused to define Nodesin the OPC UAAddressSpace. NodeClassesare derived from a common Base NodeClass. This NodeClassis defined first, followed by those used to organise the AddressSpaceand then by the NodeClassesused to represent Objects.

The NodeClassesdefined to represent Objectsfall into three categories: those used to define instances, those used to define types for those instances and those used to define data types. Subclause 6.3describes the rules for subtyping and 6.4the rules for instantiation of the type definitions.