Advanced Dimension Design - Professional SQL Server Analysis Services 2005 with MDX - page 321

Figure 8-2
Having learned about depreciation you can understand the need for custom rollup
of member values in a hierarchy to their parent — it all depends on the type of
depreciation being logged and therefore will be custom, by definition. In order to
calculate the net profit of your company, you would typically add up the sales rev-
enue, any increase in asset values, and subtract the expenditures (Cost of Goods
Sold) and depreciation values appropriately. You might be wondering if these are
just measure values, what is so complex about them. Why not just write a calcu-
lated measure appropriately? That would be a reasonable question to ask. And if
it is just measures you're dealing with, you don't have a problem.
By definition, depreciation indicates that values change over time. So,
your calculations that reflect the value of physical assets (like delivery
vans) should be adjusted for appropriate percentage changes based on
the Time dimension you are querying. Similarly, there might be other
dimensions or measure groups that calculations might depend on. For
example, say you have a Budget measure group and a Sales measure
group in your cube. Your budget for next year might depend on the
sales of the previous year and you need to use appropriate MDX expres-
sion to arrive at the budget amount. You can create such custom cal-
culations using MDX scripts with appropriate SCOPE statements, but it
will be quite a lengthy script, especially if the calculations are different
for each member in a dimension. Also, verifying that your calculations
are giving the correct values will be time-consuming. Analysis Services