DTV13 — DTV Issue: Add Necessity statements to indicate "result" of 3-way verbs

DTV has many verb concepts with three roles, where one particular role is the "result" of the verb concept. Examples are 'time interval1 plus time interval2 is time interval3', 'time interval1 to time interval2 specifies time interval3' (clause 8.2.5), 'time interval1 starts time interval2 complementing time interval3' (clause 8.2.6), 'duration3 equals duration1 plus duration2' and 'duration1 equals number times duration2' (8.3.2), etc.

Proposal: add to these verb concepts a new Necessity that identifies which role contains the "result". For example, "Necessity: Each number times each duration2 is exactly one duration1."

Motivations: (1) Add semantic knowledge that is currently not provided by the Date-Time Vocabulary; (2) When mapping DTV to OWL, this would provide the information needed to identify which role is the functional result of the verb concept. Specifically, the object property for the "result" role could be marked as an "functional object property" of the reified class that represents the 3-role verb concept.
-----------------------------

Add missing necessities for unique results

The verbs in question are about verbs that specify unique time intervals and durations in various ways. It is important for the UML and CLIF functions that the uniqueness is stated. The uniqueness is stated for all of the basic operations on time intervals. Stating the uniqueness for time interval1 to/through time interval2 is resolved by another issue. The remaining verbs in clause 8 and 9 are addressed here. Other minor errors in the text of clause 9.5 are corrected.