A virtual input transition is a special case of a general notion of virtual transition. In addition SDL have virtual save.
Transitions or saves of a process type, service type or procedure are specified to be virtual transitions or saves by means of the keyword virtual. Virtual transitions or saves may be redefined in specializations. This is indicated by transitions or saves respectively with the same (state, signal ) and with the keyword redefined or finalized.
Virtual transitions or saves must not appear in process (set of instances) definitions or in service (instance) definitions.
A state must not have more than one virtual spontaneous transition.
A redefinition in a specialization marked with redefined may in further specializations be defined differently, while a redefinition marked with finalized must not be given new definitions in further specializations.
An input or save with < virtuality > must not contain <asterisk>.
Redefinition of virtual transitions/saves corresponds closely to redefinition of virtual types.
A virtual start transition can be redefined to a new start transition.
A virtual priority input or input transition can be redefined to a new priority input or input transition or to a save.
A virtual save can be redefined to a priority input, an input transition or a save.
A virtual spontaneous transition can be redefined to a new spontaneous transition.
A virtual continuous transition can be redefined to a new continuous transition. The redefinition is indicated by the same (state,[priority]) as the redefined continuous transition. If several virtual continuous transitions exist in a state, then each of these must have a distinct priority. If only one virtual continuous transition exists in a state, the priority may be omitted.
A transition of a virtual remote procedure input transition can be redefined to a new remote procedure input transition or to a remote procedure save.
A virtual remote procedure save can be redefined to a remote procedure input transition or a remote procedure save.
The transformation for virtual input transition applies for virtual remote procedure input transition also.