PostgreSQL - a ORDBMS?

Hello!

In a german spoken python ng is a thread running about DMBMS and
Object-Databases.

I was asked - becouse of
http://www.postgresql.org/docs/8.1/interactive/preface.html#INTRO-WHATIS
- how a "object-relational database management system (ORDBMS)" ist
defined in the view of PosgreSQL, and what are the PostgeSQL features
wihch make it a ORDBMS, not just a DBMS.

Is there something other then inherance? I also found no realy good
definition of ORDBMS, the only realy good I found was some pages in
"Kemper / Eickler, Database Systems, german edition, 2004".

Lg,
AXEL.