this class manages messages indenpendently of the diagram
Declaration :
Directly inherited by : UmlMessage
Artifact : UmlBaseMessage
| Operation from | 
return the instance sending the message
Declaration :
| Operation to | 
return the instance receiving the message
Declaration :
| Operation operation | 
return the operation or 0/null,
 exclusive with form()
Declaration :
| Operation form | 
return message as a string, may be empty/null,
 exclusive with operation()
Declaration :
| Relation _from (<unidirectional association>) | 
Declaration :
| Relation _to (<unidirectional association>) | 
Declaration :
| Relation _operation (<unidirectional association>) | 
Declaration :
| Attribute _form | 
Declaration :
| Operation read_ | 
internal, don't call it
Declaration :
| Extra Class Member friend | 
Definition :
friend class UmlBaseSequenceMessage;
friend class UmlBaseCollaborationMessage;
All public operations : form , from , operation , read_ , to