UPDATE/INSERT on multiple co-dependent tables

Is it possible for an UPDATE/INSERT query string to function in such a
way that it requires two like fields in different tables to be equal
to/'in sync with' one another:

Example: I have two tables: registration & schedules....
they both record a class_id, start_date, end_date... I want to make
sure that if the schedule_id field is updated in the registration table;
that class_id, start_date & end_date fields automatically change to
match the schedules.id record in the schedules table.... I've devised a
function to handle this but pgsql recognizes the query to be 'infinitely
recursive:

CREATE RULE registration_update AS
ON UPDATE TO registration
DO
UPDATE registration SET class_id = schedules.class_id WHERE
new.schedule_id = (SELECT schedules.id FROM schedules WHERE id =
new.schedule_id);

What I'm doing is kind of redundant but necessary for
backwards-compatibility
--
www.sleekcollar.com
Ferindo Middleton, Jr.
Chief Architect
Sleekcollar Internet Application & Artistic Visualizations
ferindo(dot)middleton(at)sleekcollar(dot)com