[xml] Validating Data

[dhk <dhkuhl optonline net>]

I'm writing in C and I want to avoid writing validation rules twice. 
When I create my xml document I can validate that document against a 
schema.  However, I don't want to create the entire document and then 
find out at the end of the transaction that something is wrong.  So in 
my code I have validation functions to validate the user input. 
However, I think it should be possible to use the rules in the schema as 
the transaction is happening to validate the input.  That way I can 
alert the user and they can fix the incorrect data before the 
transaction is complete.

Does anyone know how this could be done?  Simple examples would be great 
also.

Thanks,

dave