InfoPath SP1 Preview Form Definition File Schema
With InfoPath 2003 SP1, there is a new schema for the form definition (.xsf) file, to match the features added to InfoPath.
There will be a documented roll-out of this schema, along with other InfoPath technical information, when the SP1 is officially released, but for those wanting to get a hold of the raw XSD file now, you can download the following:
(contains xsfschema.xsd.)
Disclaimer: as this schema is the InfoPath 2003 SP1 Preview schema, it is not guaranteed to be final, and might change between now and the official release of InfoPath 2003 SP1.