Need help on Data source usage

Hi guys ...Our developer has developed two sales cubes..one is built with 2lis_11_vakon &2lis_11_vaitm...another cube is built by 2lis_11_v_itm & 2lis_11_vakon...here my question is what is the diff between this two data sources vaitm & v_itm...

Can any one tell me what is the main diff between this two data sources..

regards