Update Schema W/O Invalidating Older XML Files

[yaoFeng]

Everybody,
The configuration of our system is stored in an XML file on a TTFS.
Each XML file deployed is different depending on the customer's
preferences. As we enhance the system, elements are added to or
deleted from the schema. When a customer updates his software to
obtain the enhancements, her existing XML file will fail to decode
because the file no longer matches the schema. The customer is then
forced to re-enter all his preferences. This is a problem since the
XML file is huge, about 5M. We are using an off the shelf XML to C
binder. Has anyboy else out there run into this same problem? What is
the preferred way to solve it?
Thanks to all,
Yao Feng