Design Patterns Explained: A New Perspective on Object-Oriented Design

Case Study in Variation: An International E-Tail System

Suppose an e-tail system must process sales orders in several different nations. Initially I have to handle just the United States and Canada. I look at my requirements and see several things that vary. I note these in Table 20-1.

Table 20-1. Different Cases Depending Upon Residence of Customer

Case	Procedure
U.S.A	Calculate freight based on UPS charges. Use U.S. postal rules for verifying addresses. Calculate tax based on sales and/or services depending upon locale. Handle money in U.S. $.
Canada	Calculate freight based on main Canadian shipper. Use Canadian postal rules for verifying addresses. Calculate tax based on sales and/or services depending upon Canadian province taxing rules (using ...