Self join a table to get a 1:N relationship and compare a KPI value within a dimension

Hello ,

I would like to implement a KPI showing the relationship within the element of a dimension (B) for each fixed element of a first dimension A and display it as shown below:

A | B | B (again) | KPI

 X | 2001|  2002 | 5

 X | 2001| 2003 | 2

 X | 2002| 2001 | 100

 X | 2002| 2003 | 2

.....

 Y | 2001| 2002 | 50

 Y | 2001| 2003 | 25

 Y | 2002| 2002 | 20

 Y | 2002|  2003 | 25

 ...

The aim is to be able to determine for each dimension in A, and a given fixed dimension in B, which other dimension within B is very different in terms of KPI value.

Any idea about how to inplement something like this using PQL?

Thanks for your help