Relationships
Liferay 7.4 U47+/GA47+
Relationships add fields and tables to object definitions for relating their entries with one another. This provides access to entry data in different application contexts. You can use this data in different ways. For example, in scenarios with multiple business accounts, you can use relationships with the Account system object to restrict access to custom object data by account. Or you can use aggregation fields with relationships to perform basic calculations.
Root Objects
Liferay DXP 2025.Q1+/Portal GA132+
While defining one-to-many relationships among your custom objects, you can make the parent object definition a root model in the structure by enabling inheritance.
See Using Object Inheritance for more information.