Trigger: The trigger represents a condition to start the execution of an action. There are three distinct types [13]: autonomous, player, or random. Autonomous triggers cause the action to begin automatically, without player interaction. Player triggers start actions when players carry out some operation, for example, selection of a menu item. Random triggers specify the likelihood of the action to be executed. Triggers can cause the end of the game and the calculation of a score; this is represented by the “game-ending” parameter.