[SQL] Referential integrity: broken rule?

[Franz J Fortuny]

This table:

create table things
(
  idthing integer not null,
  isthis boolean not null
  primary key(idthing,isthis)
....

)

would be referenced by this one:

create table forthings
(
  fromthing integer not null references things(idthing),

....

)

The above SHOULD NOT be accepted, since table "things" did not declare
idthing as UNIQUE. However, it IS accepted under PostgreSQL (7.0.2).

Am I wrong?

Best regards,

F J Fortuny