Object-oriented design supports inheritance over many levels of
parent, child, and grandchild classes.
Polymorphism describes the ability of a child class to supersede or ???override??? the
operation of a parent method by redefining the method on its own. Once a method
has been replaced in a child class, subsequent changes to the method in the parent
class don??™t ripple down to the child class or its descendants. In the purchase order
example, as shown in Figure 14-1, purchase orders from contracted suppliers and
suppliers not under contract inherit the methods and attributes of external purchase
orders. However, the procedure for placing the order can exhibit polymorphism
because additional approvals may be required for ordering from suppliers not under
contract.
Inheritance and polymorphism were not supported in Oracle8i objects, though the
Oracle8i database could act as persistent storage for objects, and an application
interface in an object-oriented language such as C++ or Java could add these features
to the client-side implementation of objects.
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