ISO 18629-12:2005 provides a representation of the concepts that belong to the outer core of the language, through a set of axioms and definitions. These axioms provide an axiomatization of the semantics for terminology in the ISO 18629 Outer core. The following are within the scope of ISO 18629-12:2005: * the aggregation of activities and sub-activities; * discrete activities and state; * constraints on the occurrence of activities; * concurrency for primitive activities; * complex activities; * occurrences of complex activities.