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.