A maintenance activity has a temporal region representing the total planned outage window, and another temporal region representing the actual hands-on work period.
Use this relation to associate an activity with any temporal region of interest, not only its maximal temporal extent. For example, an activity may be related to a temporal region representing a lag, a lead time, or a partial interval. The sub-property 'has temporal extent' is reserved for the maximal temporal extension of the activity.
