FUML15 — fUML should not require signal receptions

UML does not require that a model include signal receptions in order to send or accept signals. However, fUML adds the constraints SendSignalAction::fuml_send_signal_action_target_signal_reception (in 7.11.2.11) and AcceptEventAction::fuml_accept_event_receive_all_triggering_signals (in 7.11.2.2) that require the use of signal receptions for both sending and accepting signals. These constraints are entirely methodologically motivated, and they are unnecessary to the execution semantics for SendSignalActionActivation (in 8.10.2.33) or AcceptEventActionActivation (in 8.10.2.3), since both deal directly with signals (and their instances), not signal receptions.

Since UML does not itself require the use of signal receptions, they are often not use in practice by modelers, and having to add them just to be properly conformant with fUML is a nuisance. The constraints should be removed.

Remove constraints requiring receptions

It is agreed that the contraints SendSignalAction::fuml_send_signal_action_target_signal_reception and AcceptEventAction::fuml_accept_event_receive_all_triggering_signals should be removed.