Clause 5 defines the NodeClasses used to define Nodes in the OPC UA AddressSpace. NodeClasses are derived from a common Base NodeClass. This NodeClass is defined first, followed by those used to organise the AddressSpace and then by the NodeClasses used to represent Objects.

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