Connie's Convenience Store - About Peter Coad

Establishing Responsibilities for Problem-Domain Objects Connie’s Convenience Store 51
#116. “Describe Services with establishing responsibilities /
a Template” Strategy what I do (descriptions)
• Describe each service, using a template as your guide.
input, output parameters
description (including pseudo-code or actual code, detailing the algorithm to be
applied)
traceability codes to preceding documentation, if any
visibility: public, protected, private.
Here, consider what it takes to describe the “calculate total” services for sale and
for sale line item.
Using structured language, you can develop a description that looks something like
this:
sale.calcTotal ( ; total)
calcSubtotal ( ; subtotal)
calcDiscount (subtotal ; discount)
total = subtotal - discount
calcTax (total ; tax)
total = total + tax
sale.calcSubtotal ( ; subtotal)
subtotal = 0
for each saleLineItem that I know:
saleLineItem.calcSubtotal ( ; lineItemTotal)
subtotal = subtotal + lineItemTotal.
Sale line item, revisited
A sale line item may be for a sale or for a return.
Do you need any specializations of a sale line item? Check it out. A generalization
class shows “what’s the same.” A specialization class shows “what’s different.”
Consider what’s the same, what’s different. In particular, with any kind of transaction,
consider how much control, or lack of control, you have in the situation being
recorded.
You’ve got pretty good control over a purchase: you have the item, a customer
wants to buy it; you’re in control.
Returns are the real challenge: you’re getting an item you’ve had no control over;
you don’t have as much control; a lot of unusual things can happen. For example:
– A customer may return an item to a different location than where he purchased
it.
– A customer may return an item which had a different price when he
purchased it.
– A customer may return an item that Connie’s no longer carries.
– A customer may return an item that was individually marked down, perhaps
because it was slightly damaged.
– A customer may return an item and be charged a return fee.