A customer asked me : how can I link two dataproviders if the common field has an un-equal number of digits.
In one universe, the customernumber is 6 digits, in the other 8 digits - the two digits are two leading zeroes, so the zeroes can be removed without problem.
The formula I used was :
=if(Length(<customernumber>8) then SubStr(<customernumber>,3,Length<customernumber>)) Else <customernumber>
inserted into the field where the customer number was, the leading zeroes would be removed and BO would automatically agregate the data.
there is an other solution, which would involve creating a user defined object on the universe, but this would render the documents unusable to colleagues on different machines.