
110 ◾ Software Engineering: The Current Practice
of them that changes the contract may propagate to the other one. e interactions
are symmetric because the supplier can change the contract and cause secondary
modifications in the client, and vice versa.
An example of such a situation is the class Price, which is a supplier to class
Item and supplies the price of a store item. If class Price changes and now sup-
plies the price on a specific date, this change causes secondary modifications in class
Item. Figure 7.6 models the relation of two classes as a dependency on the left and
as interaction on the right.
7.2.2 Interactions Caused by Coordi ...