b/w

demand-pull

	define a target and head towards it


	fault-tolerant, if a change occurs, the system re-orientates itself 

	to continue in the new correct direction

	
		e.g.

			middle of pacific ocean, destination sydney, compass 

			heading 25o



			moved to north pacific ocean


		
			destination sydney, new compass heading 38o



			successful arrival at destination


			
		enginering systems, comp science, recovery from emmergency situations

		



supply-push

	contine forward along a specified direction


	not easily tolerant of changes in external conditions


	strong system,


	less work effort required, 


	everyday life


	some reference to the future still necessary


