how to call stored procedures with output parameters

Hello,

I am having problem with PostgreSQl syntax.
setting values anf how to call stored procedures with output parameteres.
From what I have seen by googling the subject it seems that PostgreSQL
requires that you do not provide the out parameters.

two tables

DROP SCHEMA IF EXISTS aaa CASCADE ;
CREATE SCHEMA aaa
AUTHORIZATION myuser;

CREATE TABLE aaa.principals (
pk_principal_id INTEGER NOT NULL,
principal_name CHARACTER VARYING(200) NOT NULL,
CONSTRAINT IXP_PK_PRINCIPAL_ID PRIMARY KEY (pk_principal_id)
);

CREATE TABLE aaa.credentials (
pk_credential_id INTEGER NOT NULL,
fk_principal_id INTEGER NOT NULL,
credential_value CHARACTER VARYING(254),
credential_type SMALLINT NOT NULL,
CONSTRAINT IXP_PK_CREDENTIAL_ID PRIMARY KEY (pk_credential_id),
CONSTRAINT FK_AAA_CREDENTIAL_1 FOREIGN KEY (fk_principal_id)
REFERENCES aaa.principals (pk_principal_id) ON DELETE CASCADE
);

a few things I am trying to do and they do not work

CREATE OR REPLACE FUNCTION aaa.unlock_principal(p_pk_principal_id_in IN
aaa.principals.pk_principal_id%TYPE)
RETURNS void
AS $BODY$
BEGIN
UPDATE aaa.principals SET aaa.principals.is_unlocked = TRUE
WHERE aaa.principals.pk_principal_id = p_pk_principal_id_in;
END;
$BODY$ LANGUAGE plpgsql VOLATILE;

ALTER FUNCTION aaa.unlock_principal(aaa.principals.pk_principal_id%TYPE)
OWNER TO myuser;

I am calling this function from the console like this

SELECT aaa.unlock_principal(10);

In this function it seems that aaa.principals.is_unlocked is wrong.
What are the rules for fully qualifying the name of a field or a table?

I also have the following

CREATE OR REPLACE FUNCTION aaa.validate_credential (
p_pk_principal_id_in IN aaa.principals.pk_principal_id%TYPE,
p_credential_type_in IN aaa.credentials.credential_type%TYPE,
p_credential_value_in IN aaa.credentials.credential_value%TYPE,
p_return_code_out OUT INTEGER)
AS $BODY$
DECLARE
v_credential_value aaa.credentials.credential_value%TYPE;
BEGIN
p_return_code_out := 0; -- C_OPERATION_SUCCESFULL;

BEGIN
SELECT credential_value INTO STRICT v_credential_value FROM
aaa.credentials
WHERE fk_principal_id = p_pk_principal_id_in AND
credential_type = p_credential_type_in;
EXCEPTION
WHEN TOO_MANY_ROWS THEN
p_return_code_out := 3; -- C_TOO_MANY_ROWS; -- too many rows with
same id, consistency problem
RETURN;
WHEN NO_DATA_FOUND THEN
p_return_code_out := 42; -- C_CREDENTIAL_DOES_NOT_EXIST;
RETURN;
END;

IF v_credential_value <> p_credential_value_in THEN
p_return_code_out := 44; -- C_WRONG_CREDENTIAL; -- wrong password
RETURN;
END IF;

END;
$BODY$ LANGUAGE plpgsql VOLATILE;

the questions here are
how do I call this function from the console?
e.g. in MySQL you just define a variable @return as the out parameter
call aaa.validate_credential(10, 0, 'user', @return);

what is the right syntax in PostgreSQL?

how do I call this function form inside another function?

If a function has 3 out parameters , e.g
CREATE OR REPLACE FUNCTION aaa.authenticate (
p_name_in IN aaa.principals.principal_name %TYPE,
p_passwd_in IN aaa.credentials.credential_value%TYPE,
p_pk_principal_id_out OUT aaa.principals.pk_principal_id%TYPE,
p_groups_out OUT refcursor,
p_return_code_out OUT INTEGER)

how do I call this from the psql console and how do I call this function
form inside another function?

thank you

Nikolas