Depending on referential integrities ZPostgresUtils generates a database diagram.
At this time ZPostgresUtils is a ZClass based product.
It works with RDBMS PostgreSQL 7.0 or later.

Assuming you setup the following tables ...

CREATE TABLE title (
 titleid SERIAL NOT NULL,
 title character varying(50))

CREATE TABLE customer (
 customerid SERIAL NOT NULL,
 name character varying(75),
 city character varying(50),
 street character varying(75),
 phone character varying(20),
 fax character varying(20))

CREATE TABLE orders (
 orderid SERIAL NOT NULL,
 customerid int4 NOT NULL REFERENCES customer (customerid) ON DELETE RESTRICT ON UPDATE CASCADE INITIALLY DEFERRED,
 what character varying(60),
 deadline date)

CREATE TABLE invoice (
 invoiceid SERIAL NOT NULL,
 orderid int4 NOT NULL CONSTRAINT fororders REFERENCES orders (orderid) MATCH FULL ON DELETE RESTRICT ON UPDATE CASCADE,
 amount float8)

... you will get this output:

Tables and Views with referential integrity definition

customer
customerid	orders orderid invoice invoiceid orderid amount customerid what deadline	name	city	street	phone	fax