Connie's Convenience Store - About Peter Coad

66 Connie’s Convenience Store Selecting Human-Interaction objects
Wow!
By now, you know how to read a scenario view.
This scenario view expands upon these two lines from the previous rounds:
The “calcTotal” service invokes the “calcTax” service.
The “calcTax” service returns “totalTax.”
Here’s what happens now:
Within a sale object, the “calcTotal” service invokes the “calcTax” service.
The “calcTax” service sends a “getTaxCat” message to a store object.
A store is told to get its tax categories.
The “getTaxCat” service returns a collection of tax categories.
The “calcTax” service sends a “howMuchTaxInCat” message to a sale line
item object (and it may do this a number of times), giving it a tax
category.
A sale line item is told to calculate its tax for a given category.
The “howMuchInTaxCat” service sends a “howMuchInTaxCat”
message to an item object, giving it a tax category.
An item object is told to calculate its amount within a tax category.
The “howMuchInTaxCat” service invokes the “getPriceForDate”
service, giving it a date.
The “getPriceForDate” service returns a price.
The “howMuchInTaxCat” service returns an amount.
The “howMuchInTaxCat” service returns a tax amount.
The “getTaxRate” service returns a tax rate for that category.
The “calcTax” service returns “totalTax.”
Yes!
Scenarios are vitally important for building effective object models. You work out
system dynamics. And you find additional objects and responsibilities along the way.
What a deal!
SELECTING HUMAN-INTERACTION OBJECTS
Finally, you are ready to check out some human-interaction objects.
Actually, you might choose to find human-interaction objects; then you could work
on problem-domain objects next. Or you might work back and forth, finding objects
and dropping them into the HI or PD “buckets.” Anyway, at this point it’s time to check
out some human-interaction objects. In today’s systems, human-interaction objects are
most often windows or reports.
Select windows
What windows should you consider?