using tuple in cognos

[DhimanBiswas]

I have a scenario where I have a crosstab with ProductCategory in the row edge, Year/Quarter in the column edge. I would take the measure to be OrderQuantity. Now what I need is something like this :


                    2006 - Q1   2006 - Q2           2006 - Q3           Variance Q1 vs Q2        Variance Q2 vs Q3
                    OrderQty           OrderQty           OrderQty           OrderQty                        OrderQty
Bikes                   
Accessories                   
Clothing                   
Components

The Year and Quarter values comes from 2 different prompts. The columns for variance is displayed ONLY when the user selects MORE THAN 1 CONSECUTIVE quarters. So I have decided to first create derived data items having Order Quantity for all the 4 quarters, then displaying them based on conditions as per prompt selection. My package is a DMR model.
1) I am able to write the expression for OrderQuantity for a Quarter in a derived data item as :
tuple ([OrderQuantity] , [1] , currentMember ( [Dimensional View].[Product].[Product] ) )
So here '1' indicates the first quarter. Similarly I have created derived data items for the other Quarters. But this '1', '2', '3' and '4' are essentially 'Members' that CAN be fetched only from one of the Year levels in the hierarchy. So that makes it static ( belonging to only one Year value).
When I write the expression as :
tuple ( [OrderQuantity] ,
currentMember ( hierarchy ( member ( [Qtr1] , 'OrderQuantity_Qtr1', 'OrderQuantity_Qtr1', [Dimensional View].[Date].[Date] ) ) ) , currentMember ( [Dimensional View].[Product].[Product] ) )
where [Qtr1] is a data item having value 1 (which indicates 1st quarter being fetched by substring function on prompt value). The output is

                 1           2           3           4
                 OrderQty   OrderQty   OrderQty   OrderQty
Bikes         3250           3700   8285   6996
Accessories    397           934           7828   4717
Clothing         734           1218   8676   6299
Components  245            577           2625   1760
                   

which is the same when I simply use tuple ( [OrderQuantity] ). Hence I am not getting values for individual quarters by this way. Removing the currentMember and Hierarchy functions from the [Qtr1] yields no result.
Any idea?