In our simple example (see Chapter 2) we defined a single domain object BusinessPartner. This class was then enhanced according to its persistence descriptor. The enhanced class implements the PersistenceCapable interface and provides implementations of all the PersistenceCapable methods. We then used the enhanced class in our application.
The term JDO instance is used to describe any instance of a Java language class which implements the PersistenceCapable interface which the implementation is capable of managing. Some implementations, largely dictated by the underlying data store, require storage areas to be explicitly defined for each class before that class can be managed. This is more typical of object-relational mapping implementations (with an underlying relational database) than of object databases.