Issue 221: Dual events

Posted by vladimir.alexiev on 21/11/2012 

There are several examples of "dual events" in CRM: 
- E8 Acquisition: transferred title from; transferred title to 
- E9 Move: moved from; moved to 
- E10 Transfer of Custody: custody surrendered by; custody received by 
- E15 Identifier Assignment: assigned, deassigned 
- E81 Transformation: transformed; resulted in 
- E80 Part Removal: removed & diminished; E79 Part Addition: added & augmented 

I think that Part Removal and Part Addition should be merged. 

This will allow more consistent modeling of the following situations: 

- moving an object from one collection to another (similar to E8 and E10): 

removed=added=<object>, diminished=<old_collection>, augmented=<new_collection> 

- replacing a part of an object (similar to E81): 

removed=<old_part>, added=<new_part>, diminished=augmented=<object> 
This is due to uniqueness of an object by virtue of the schema (type) of the whole. 

separate because there is no assumption that the part removed exist before and after.