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.