Hi,
Thank you very much for your comments.
What do you meant by "opening balance"? Is it Initial Stock Balance or Opening Balance of partcular period?
If the answer is "Opening Balance of partcular period", I would like to know how could you get this beside of doing something like closing stock ?

>>one retrieves "closing balances" for one given period, adds in the transactions for a given period, and arrives at a "closing balance" for the given period.

How to retrieve the "closing balances" for one given period? Is it re-calculate the stock balance from beginning?
What Happend if some of the transactions purged? It may get the wrong result.

Thank you again for your comments.