iPod Cover Art itc and Persistent ID

Hello

I have a short question linked to iTunes 7 and the directory Album Artwork.
One member in a forum said :

These are Persistent IDs, which you can find in iTunes Music Library.xml and folder structure is like this:

Library Persistent ID -> decimal value of last hex digit in tracks persistent ID -> dec value of before last hex digit -> dec value of 3rd hex digit from the end -> Library persistent ID - Track persistent ID .itc

F3AF81BA9C7F669C -> 05 -> 03 -> 10 -> F3AF81BA9C7F669C-5C5970C9B6116A35.itc

Click to expand...

from : http://forums.macosxhints.com/showthread.php?p=325382

I understood the directory tree structure, but I've tried to figure out how this could work, and I can't understand how the Itunes Library.xml and the Persistent ID are linking to the correct .itc file.

Can someone explain me how the link mechanism between the Persistent ID and the .itc File works ?
I couldn't find more explanations on the web...

Thx a lot for your help !
MatD