A different twist on the aggregation of calculated measures in SSAS - ssas

Question

I have to count something in a strange way, and it works in most cases -- both at leaves and at higher levels of aggregation across multiple dimensions. But it doesn't give correctly aggregated values for one specific dimension.
What I have at the moment is ...
CREATE MEMBER CURRENTCUBE.[Measures].[Active Commitments]
AS NULL,
FORMAT_STRING = '#,#',
VISIBLE = 1;
SCOPE (DESCENDANTS([Date Dimension].[Fiscal Year Hierarchy],,AFTER));
[Measures].[Active Commitments] =
iif([Constituent Activity].[Type].currentMember.Properties("Name")="Correspondence",
sum(([Commitment Dates].[Start Date], NULL: [Date Dimension].[Fiscal Year Hierarchy]), [Measures].[Commitment Count]),
sum(([Commitment Dates].[First Funded Date], NULL: [Date Dimension].[Fiscal Year Hierarchy]), [Measures].[Commitment Count]))
- sum(([Commitment Dates].[Stop Date],[Commitment].[Was Commitment Ever Active].[Sometime Active], NULL: [Date Dimension].[Fiscal Year Hierarchy]), [Measures].[Commitment Count]);
END SCOPE;
SCOPE (DESCENDANTS([Date Dimension].[Fiscal Year Hierarchy],,AFTER));
<Similar to above>
As you can see, the complexity is that one type of "commitment" commences at the [Start Date] and others commence at the [First Funded Date].
This fails whenever multiple members of [Constituent Activity] are selected because in such cases the use of currentMember in the SCOPE statement is invalid. For example, the following MDX executes successfully but outputs #Error --
select
[Measures].[Active Commitments] on columns
,[Date Dimension].[Fiscal Year Hierarchy].[Fiscal Year].&[2011\12] on rows
from Compass3
where
{[Constituent Activity].[Description].[XYZ]
,[Constituent Activity].[Description].[ABC]}
I think what I need to encode within the SCOPE statement is the recursive ...
if a single member of [Constituent Activity] is current
then use the calc as defined above
else use [Measures].[Active Commitments] = sum(all selected members of [Constituent Activity], [Measures].[Active Commitments])
... but how would I write that?

Answer 1

Do you have control all the way back to the data warehouse/data source view? Can you add a calculated field to your fact table, so you have [Commitment Active Date] at the cell level? Then you could do much simpler counts in the cube.
I have found that enforcing business rules and doing business calculations in the data warehouse is more efficient and easier in the long run.