Please forgive this non-Postgress user, but when you say Object Oriented RDBMS, do you mean the DBMS' source code is written in OO (C++/Smalltalk/etc) or do you mean the data is stored as objects? If the latter, I suggest you do not call Postgress a RDBMS (Relational Database Management System). Storing data as objects in the DB qualifies as an OODBMS.
Please forgive this non-Postgress user, but when you say Object Oriented RDBMS, do you mean the DBMS' source code is written in OO (C++/Smalltalk/etc) or do you mean the data is stored as objects? If the latter, I suggest you do not call Postgress a RDBMS (Relational Database Management System). Storing data as objects in the DB qualifies as an OODBMS.