Unique or Primary Key?

This table is man-in-the-middle of a many-to-many relationship:

CREATE TABLE cv_entries (
subscriber INTEGER NOT NULL
REFERENCES subscribers
ON DELETE CASCADE
ON UPDATE CASCADE,
entry_type INTEGER NOT NULL
REFERENCES cv_entry_types
ON DELETE CASCADE
ON UPDATE CASCADE,
ordinal INTEGER,
value1 TEXT,
value2 TEXT,
minimum_trust SMALLINT,
UNIQUE(subscriber, entry_type, ordinal)
);

I used a unique index here because I couldn't see any reason for a
Primary Key - this table will always be searched on either the
subscriber or entry_type index.

Was I wrong? Should this be a Primary Key?

--
Bruce

Bitterly it mathinketh me, that I spent mine wholle lyf in the lists
against the ignorant.
-- Roger Bacon, "Doctor Mirabilis"