Why are you trying to replicate database functionality in something that patently isn't a database? There are a million database alternatives, assuming you don't want to (or can't) use MySQL. Every single one of them will generate a unique ID for you and manage it for you. You wouldn't even have to know it's there (other than setting it up).

Get it straight, people - XML is not a database!

------
We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.