Hi Steve,
From your example, it seems to me that something called "AmountAccruedYTD" would be derived from whatever it is that is being accrued.
From your description, I assume that each "deduction instance" is uniquely identified somewhere.
So it would seem to be a matter of "just" adding up the deductions between two points in time (e.g. "CurrentAccountingYearStartDate" and "CurrentAccrualCutoffDate") and putting the result into the "Amount AccruedYTD" column.
Derivation is discussed extensively in the Big Brown Book (e.g. pages 98 onwards) and in NORMA Tutorial 2 which you can download from the library.
Also, there are quite a number of posts on this site about derivation. (e.g. try a site search using "derived".)
I don't think that "automatic derivation" is yet implemented in NORMA so we currently advise a textual annotation on the model.
Hope this helps
Ken