Calculated Values And Database Design.

Hi everybody,

I need some help on calculated values in my database design.

I'm creating an accounting / business management application with the
usual modules like A/R, A/P, Inventory, etc.

I don't know how to handle calculated values in fields like "Customer
Balance", "Inventory Item Qty on Hand", "Inventory Item Qty Last cost"
and other similar.

I don't want to create fields in the database to store these values
but I want to create them on the fly instead. Another thing I prefer
to do is use code in my application (vb.net) not T-SQL to do this
(stored procedure or views), because this way I'm moving business
logic into SQL; so far all the logic is located in a Business Rules
DLL.

My question is how can I do that and at the same time achieve "easy"
joins.

For example:
Every time I retrieve some customer's info I need his balance. Let's
say if my query is:

SELECT CustomerID, CustomerName, Address from Customers
Where CustomerID = ‘xxxxxx'

How can I retrieve the balance, when is calculated from other fields
in other tables, such as Invoices, Credit Memos and Cash Receipts?

I thought to use views and add a join to the above query. Is that good
or bad, performance wise?

What other options I have?

Looking forward for your answer.

Thanks in advanced.
Stefanos