Connected transformation is connected to other transformations or directly to target table in the mapping. An unconnected transformation is not connected to other transformations in the mapping. It is called within another transformation, and returns a value to that transformation. Connected lookup receives input values directly from mapping pipeline whereas UnConnected lookup receives values from: LKP expression from another transformation. Connected lookup returns multiple columns from the same row whereas UnConnected lookup has one return port and returns one column from each row. Connected lookup supports user-defined default values whereas UnConnected lookup does not support user defined values.