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
differenttables to be equal to/'in sync with' one another: <br /><br /> Example: I have two tables: registration &
schedules....<br /> they both record a class_id, start_date,  end_date... I want to make sure that if the schedule_id
fieldis updated in the registration table; that class_id, start_date & end_date fields automatically change to
matchthe schedules.id record in the schedules table.... I've devised a function to handle this but pgsql recognizes the
queryto be 'infinitely recursive:<br /><br /> CREATE RULE registration_update AS<br /> ON UPDATE TO registration<br />
DO<br/> UPDATE registration SET class_id = schedules.class_id WHERE new.schedule_id = (SELECT schedules.id FROM
schedulesWHERE id = new.schedule_id);<br /><br /> What I'm doing is kind of redundant but necessary for
backwards-compatibility<br/><table cellpadding="0" cellspacing="0" width="100%"><tr><td> -- <br />
www.sleekcollar.com<br/> Ferindo Middleton, Jr.<br /> Chief Architect<br /> Sleekcollar Internet Application &
ArtisticVisualizations<br /><a
href="mailto:ferindo.middleton@sleekcollar.com"><u>ferindo.middleton@sleekcollar.com</u></a></td></tr></table>