The query is : "Find cars in a region five hours before it is covered by a flood." From the ontological knowledge base the appropriate sources such as video source, flood meter, etc. are identified. The query can then be constructed.

SELECT object
CLUSTER *
FROM { UNION( SELECT object
		  CLUSTER * ALIAS OBJ1
		  FROM { 	SELECT t
				CLUSTER * 
				FROM video_source }
		  SELECT object
		  CLUSTER * ALIAS OBJ2
		  FROM { 	SELECT t
				CLUSTER *
				FROM flood_meter } ) }
  	WHERE OBJ1.type='car' AND OBJ2.type = 'starting_flood' 
  	AND OBJ1.t = OBJ2.t - 5 }
WHERE object.type= 'car'