SAP BW DSO lookup

Hi Guru's

can you help me with the coding.

Scenario :

I have two DSO'S .

1) DSO 1  :    has 3 fields say

FIELD A ,  FIELD B ,  FIELD C.  

2) DSO 2  has 3 fields say

FIELD D , FIELD E , FIELD F.                                       

logic :

when field B , field E are equal and field C and field F are equal. 

then field A values should be mapped to field  D