Connected vs. Unconnected Lookups

CONNECTED LOOKUP	UNCONNECTED LOOKUP
Part of the mapping data flow	Separate from the mapping data flow
Returns multiple values (by linking output ports to another transformation)	Returns one value (by checking the Return (R) port option for the output port that provides the return value)
Executed for every record passing through the transformation	Only executed when the lookup function is called
More visible, shows where the lookup values are used	Less visible, as the lookup is called from an expression within another transformation
Default values are used	Default values are ignored