Sharing session data with Perl

Is there a published spec of the format of the session data string? It would greatly simplify one of my applications if I could share data between PHP and Perl using sessions. Since I use MySQL to store session information, it would be trivial for me to make a call to a Perl script with a session id, and, within Perl, grab the session data, parse it, use it, perhaps even change it, and then return control back to my PHP application. So, if I knew the exact format of the data string, I could avoid having to try to guess at its structure, and write a Perl routine to decode it and store it in a session hash... Has anyone tried this before? Thanks .