pop-up box in PL/SQL

I have a suite (fascicule?) of pages to maintain some database tables containing vehicle information. When the end user enters or changes data on his vehicle I want a little box to pop up to tell him that the change has been effected, the kind of thing that can be done with msgbox in VBA. This can be done with the procedure message in the PL/SQL components of Oracle Forms, but I am working on a web page and SQL*Plus demands that I define message. What procedure should I be using?