ScheduleRevisionTrigger

These are all the IATA message types. Please see the IATA SSIM manual for an exact definition, or below for a short explanation. 

NEW = new flight
CNL = cancel flight
RPL = multiple changes to same flight, eg TIM+EQT
SKD = schedule update
ACK = acknowledgement
ADM = Change of Existing Information Expressed by the Use of Data Element Identifier Only
CON = Change of Aircraft Configuration/Version
EQT = Change of Equipment Information
FLT = Change of Flight Designator
NAC = Not Actioned
REV = Revision of Period of Operation and/or Day(s) of Operation
RSD = Request for Schedule Data
TIM = Change of Time Information
RRT = Change of Routing
RIN = Reinstatement

And then we have a few internal ones for N-OC:

DayMove = When a flight change day of operation after day move with adhoc edit
ScheduleSplit = After a schedule is split using adhoc edit or schedule edit
ProjectChange = When a change to a project is done (adding, removing, changing)