You must create class-level relationships before you can perform the following tasks:

You do not have to create class-level relationships to create lineage associations between custom objects and other objects through linking rules or enumerated links.

Create class-level relationships so that you can define relationships between individual metadata objects. For example, you create a custom model that contains the DataStructure class. You want to relate objects of the DataStructure class with objects of the Oracle Table class. First create a class-level relationship between the DataStructure class and the Oracle Table class. You can then create object-level relationships between any object of the DataStructure class and any Oracle table.