When I use the word "above" I mean "layers" of code. So if an Object-database was implemented by using a relational database, it would be "above" the layer of t

When I use the word "above" I mean "layers" of code. So if an Object-database was implemented by using a relational database, it would be "above" the layer of the RDBMs. I think that is what object-to-relational mappers like Hibernate do. I think it would seem quite natural to implement objects on top of, with the help of an RDBMS. But not sure if the opposite is true.