First... DESIGN IT, completely. Absolutely ignore all considerations of "how," and include technical requirements such as XML along with all other user-requirements. Write them down. Review them with your client or boss or the internal client or whatever.

Next, "there's more than one way to do it," and plenty of high level frameworks exist: review them carefully, and spend more than one day on each one. Construct a good working-pattern for how you would actually approach this in each of several cases.

Some frameworks, like CGI::Application, are low-level whereas others such as Catalyst or Gantry are high. Apache has lots of XML-based app servers.

By all means, give very serious consideration to the very real possibility that you will wind up not having to write any new custom-code at all! The odds are extremely good that, if you look hard and long enough, the "wheel" you want already exists.