The manufacturer or system integrator of a Compressed Air System may wish to add Variables, Objects, or Methods which are not yet defined by this specification. In such a case the additional Variables, Objects, or Methods shall be added to an appropriate FunctionalGroup of the Component. It is important, that the Variables, Objects, or Methods which are added match the description of the FunctionalGroup they are added to. If there is no FunctionalGroup available the Variables, Objects, and Methods fit in, the manufacturer or system integrator shall create a new Object of the FunctionalGroupType.
It is also possible to define a subtype of the FunctionalGroupType or one of its subtypes to define a new collection of Variables, Objects, or Methods. When subtyping, the manufacturer or system integrator should keep in mind, that all Variables, Objects, and Methods of the supertype are also available to the new subtype.
In general, no new Variables, Objects, or Methods shall be created that are already available in this specification. If the manufacturer or system integrator wants to add already existing Variables, Objects, or Methods to another FunctionalGroup, the Organizes ReferenceType shall be used.
When creating Variables which are representing Quantities, the BaseAnalogType or one of its subtypes shall be used as TypeDefinition. When creating Variable which are not representing Quantities, the DataItemType or one of its subtypes, other than the BaseAnalogType, shall be used as TypeDefinition. Either way, the Definition Property shall be instantiated to further clarify the intended purpose of the Variable.
Figure 12 illustrates some usage examples on how to extend FunctionalGroups of a compressor.