URIs don't necessarily map onto file names. You can set your web server to do just about anything given a certain URI. You might have a script run for just about anything, and there are several ways that you can make this happen, such as URI rewriting, default file names, mod_perl handlers, and so on.

Along with that, you can add a query string (that stuff after the ?) to any HTTP URI. It doesn't matter if it's a script or regular file.

How you actually set it up depends on your webserver, and isn't anything to do with Perl.