Substract as an aggregation rule for different level in a DIM ?!

Question

Hi there..
I'm building a BI model based on financial transactions (incomes, expenses, etc..)
and my main problem is how to substract a measure, where the aggregation rule is set to SUM, for different levels in the "Account" dimension?
Example:
I have the "Account" dimension with the following hierarchy:
Account_ID / Account_name / Account_type / Account_total
And, lets say, 2 rows in it:
1.row in the "Account" dimension:
account_ID : 100
account_name : "Marketing expense"
account_type : "Variable expenses"
account_total : "Total profit" (total income - total Expenses)
2. row in the "Account" dimension:
account_ID : 200
account_name : "Financial incomes"
account_type : "Total incomes"
account_total : "Total profit" (total income - total Expenses)
"Total profit"
"Tot. incomes" "Tot. Expenses"
"Finan. incomes" "Market. expenses"
The fact table has just one measure: "Amount" and, of course, some foreign keys:
Account_ID -> "Account" dim
Organization_ID -> "Organization" dim
Date -> "Date" dim
Amount
The measure "Amount" in the fact table is positive both for expenses and incomes.
Now, what I'm trying to do is to sum up that measure on my top level in the "Account" dim.
At that level my report in Answers should substract "Total expenses" from "Total incomes"!
How can I do that?
thanks..
Ivan

Answer 1

Sorry to pop the obvious question, but can't you model that nicely and put it into distinct columns?
If not, you can create derived measures on you fact using "case when" statements. One for the incomes with amount > 0 (or >=0 ...depends on where you want to have the 0's) and one for the expenses with amount < 0.
HTH,
Chris