5.3 Entities and Relationships
The Logical Modeler only allows meaningful relationships to be defined for a given source entity type and target entity type. For example, a Parent/Child relationship can only be used by Data and External entities. An Includes relationship can only use Conceptual entities as the target entity. The Modeler helps to validate the model and your design based on these relationship rules.
For more details about these rules, refer to 7.4 Relationships and Entities