When setting up a database, we usually add two columns to let us track editing in postgis/postgresql.
alter table schema.table add column edituser char(24);
alter table schema.table add column editdate timestamp;
CREATE OR REPLACE FUNCTION update_edit_func()
RETURNS TRIGGER AS '
BEGIN
NEW.edituser = current_user;
NEW.editdate = current_timestamp;
RETURN NEW;
END;
' language 'plpgsql';
CREATE TRIGGER trigger_name BEFORE insert or update
ON schema.table FOR EACH ROW EXECUTE PROCEDURE
update_edit_func();