Code:
 Original data set
Descr2    Descr1    Data1    Data2    Data3
          Alpha       1        2        X
          Bravo       3        4        Y
          Charlie     1                 X
          Delta       1        2        X
          Sigma       5        9     
1         Sigma       5        9        Z
=======================================
Then sorted by data1,data2,data3  and adding an index that increments with changes in the data.

Descr2    Descr1    Data1    Data2    Data3    index
          Alpha      1         2         X       1
          Delta      1         2         X       1
          Charlie    1                   X       2
          Bravo      3         4         Y       3
1         Sigma      5         9         Z       4
          Sigma      5         9                 5
========================================
Finally list the description pairs  that exhibit common data sets (index values)
1 -  |Alpha,  |Delta
2 -  |Charlie
3 -  |Bravo
4 - 1|Sigma
5 -  |Sigma



That's how I understand the problem.
_________________________
Glenn