VariableTypes are used to define the substructure, semantic and DataType of Variables. Defining VariableTypes only makes sense, if it is expected that the VariableType is used several times. Variables are typically defined in the context of an ObjectType which already defines the semantic of the Variable. Therefore, often the VariableTypes of the base specification (specifically OPC 10000-8 with VariableTypes providing ranges and engineering unit) are sufficient and no new VariableTypes need to be defined.