Xml Based Shoping Cart in php

Heloo Guyz need little help from you i am making product display website from xml

its basically get product data from online xml file and show it in our website ... i do everything fetching data ETc.. now i need shoping cart thing in my site

please any one suggest me any script or tell me how to do this ...

because every shoping cart i found on google its based on database system but my files coming from xml file feed

so please help me in this

thank you in advanced waiting for your reply