The section defines common variable types that are used by multiple section of the ISA specification (i.e. equipment and physical assets etc.) In some cases these types define a generic version of the variable that will be further customized in the specific section, i.e. equipment or physical asset variable section.
The variable types defined in the following sections make use of reference types that are defined in section 9. These reference types provide specific semantic information. To fully understand the Variable or Object models it may be required to review these reference descriptions.