PRIMARY KEY & INHERITANCE (fwd)

Hi,

please look at following example:

CREATE TABLE picture (
id serial not null,
description text,
filename text);

CREATE TABLE advert (
artist text,
customer text,
target text)
INHERITS (picture);

CREATE TABLE work (
id serial not null,
advert_id int4 not null references advert,
value numeric(6,2) default 0);

NOTICE: CREATE TABLE will create implicit sequence 'work_id_seq' for SERIAL
col
umn 'work.id'
NOTICE: CREATE TABLE/UNIQUE will create implicit index 'work_id_key' for
table
'work'
NOTICE: CREATE TABLE will create implicit trigger(s) for FOREIGN KEY check(s)
ERROR: PRIMARY KEY for referenced table "advert" not found

How can I create PRIMARY KEY CONSTRAINT for table advert?

Thank you in advance for any reply, \fer