Connie's Convenience Store - About Peter Coad

Working Out Data-Management Dynamics with Scenarios Connie’s Convenience Store 89
Begin with a search need from the PD component.
Here, consider a search need from a PD object:
store.getCashierForID
store.getItemForUPC.
Work out the dynamics for interacting with DM objects.
Scenario: get cashier for number
Here you go again. For this scenario, you need a “cashier DM” object. That object
knows how to use the local file system to efficiently find the cashier object for the
number. Here is the scenario view (Figure 1–62):
Store
Figure 1–62: The “get cashier for number” scenario view.
Note that the basic search service, one that all DM objects provide, is made specific
in the scenario view, using “search on .”
Scenario: get item for UPC
This time, you’ll need an “item DM” object.
The item DM knows how to use the local file system to efficiently find the item object
for the UPC.
Here is the scenario view (Figure 1–63):
Store
CashierDM
getCashierForNumber searchOnNumber
getCashierForNumber store.getCashierForNumber (number ; cashier)
searchOnNumber
ItemDM
getItemForUPC searchOnUPC
Scenario: get item for UPC.
Scenario constraint:
0.1 seconds, 9 out of 10 times,
0.5 seconds max.
getItemForUPC store.getItemForUPC (upc ; item)
searchOnUPC
Scenario: get cashier for number.
Scenario constraint:
0.1 seconds, 9 out of 10 times,
0.5 seconds max.
cashierDM.searchOnNumber (number ; cashier)
itemDM.searchOnUPC (upc ; item)
Figure 1–63: The “get cashier for id” scenario view.