Mapping fields of extract structure to infocube

hi Gurus,

I have question related to mapping fields of a extract structure to infocube

Taking 2LIS_11_VAITM as an example. This DS will have many fields but what if the infocube relevant to this DS need only few fields out them???? do I have to map the fields in the transfer sturctue of insource manually according to the cube?????? In that case what if i wanna use the same Infosource to another infocube having different dimensions....I am confused GURUS help me out plzzzzz.