The Object-Relational (OR) model is very similar to the relational model; however, it treats every entity as an object (instance of a class), and a relationship as an inheritance. Some features and benefits of an Object-Relational model are:
• Support for complex, user defined types • Object inheritance • Extensible objects
(Database Fundamentals. Sharma, N. et al. DB2university.com, 1ª. edição, 2010)