Connie's Convenience Store - About Peter Coad

Establishing Responsibilities for Problem-Domain Objects Connie’s Convenience Store 39
Responsibilities for tangible things
Establish responsibilities for tangible things in the store:
– item
– register
– cash drawer
and
– tax category.
You’ll work on sale and other transactions, immediately after that.
Item
Establish responsibilities: “what I know.”
An actual item is described by its item number, description, universal product code
(UPC), expiration date, price, and whether it’s taxable or not.
An item object “knows” its values for those same attributes (Figure 1–25):
– number
– description
– UPCs
– prices
– taxable (either it’s taxable or it’s not).
number
description
UPCs
prices
taxable
Figure 1–25: Item: “what I know.”
Wait a minute!
Some of these attributes seem to have repeating values. That’s a good place to look
for additional objects.
Consider UPC
An item object potentially knows a collection of UPC values.
Using an attribute which has a number of repeating values is not a problem.
Item