When you first create a BC4J project, you have an option to create entity objects from your schema objects. Associations will be created for any underlying foreign keys in the database. However, you can add additional associations later.
To create an association:
While the project is selected, choose File | New, click Business Components, and double-click Association.
To edit an existing association, in the Navigator, right-click the associateion and choose Edit. Or simply double-click the association.
Ways to Create Entity
Objects and Associations
About Generating Entity
Objects, Associations, and Database Tables