Understanding the Model Layer - Oracle ADF 11gR2 Development Beginner's Guide - page 63

You can verify the creaion of the atributes in the DeptEO.xml file and compare the columns
in the DEPT table.
Have a go hero - set the primary key for the EmpEO.xml file
Now we have two enity objects in our com.empdirectory.model.entity package—one
is EmpEO.xml and the other is DeptEO.xml file. We have set the Deptno atribute as the
primary key for DeptEO.xml .
We have not created a separate Rowid atribute to represent a primary key for the enity
object. So, now it's your job to set the Empno as a primary key for the EmpEO.xml ile.
Bravo! You have set the Empno as the primary key. Now we have two atributes as the primary
key. Don't worry about that right now; we will take care of this later as we proceed.
Why association?
As the name suggests, associaion is used to associate enity objects. When you look closely
at the EMP table, you will find a DEPTNO column. In database terms, it is called a foreign key
because DEPTNO is the primary key for the DEPT table. The foreign key associaion for enity
objects is done using associaions.
The usage of associaion is exactly as that of a foreign key in a relaional database for
maintaining referenial integrity. When the database has a foreign key constraint, the
associaion is created automaically by ADF. The following screenshot explains the
relaionship between the EMP and DEPT table through Deptno :