hidden values

Maintaining state with hidden fields in forms

It is common to need to break a form up into multiple pieces from time-to-time. This is often done when the second page of the form depends on information submitted on the first page. For example, consider the schedule of classes that BannerWeb displays. The first form asks you to pick a semester, then you hit submit, then the next page asks for the department to list classes for, then you hit submit again, then you get a list of classes for that semester and department combination.

Here is the exchange of information between browser (the client) and the server:

Client                                                       Server
===================================================================

Client requests schedule of classes ----------------------->

        <-----------  Server sends back list of possible semesters,
                                         including blank HTML form.

Client fills out form (drop down of 
semester) and sends to server   ---------------------------->

         <----------  Server reads semester variable from form, 
                      sends list of departments for that semester.

Client picks from list of departments,
but when they submit the form, how do
they send the semester again?  The server
has forgotten it!  ----------------------------------------->

                      Server needs to know both semester and 
                      department here.