about PostgreSQL...(important)

Hi to all:   I have a question.   PostgreSQL is Object-Relational DBMS . Can I progam Object-Oriented
Language for PostgreSQL?

Example:   I create two tables:               create table Address(                             street char(20),
                    city char(20),                             province char(20)                );
 
                create table students(                                no int4,                                name
char(8),                               address  Address,               )              insert into Address values
('ZHONG-SHAN','TAIPEI','TAIWAN');
   I find the Address record's oid:           =>  select oid from Address where province='TAIWAN';
                              oid                            --------                             28672   Then, I
inserta record to students table:           =>  insert into students values (8852,'John',28672::Address);
 
  Finally, I select the  record about the student's province depend on oid:           =>select no,name,address.province
fromstudents;
 
  BUT PostgreSQL's message is error,why?

Thank you.....                Frank