At this time, Xalan is not set up to request schema validation when it instantiates its own copy of the parser. There probably ought to be a way to pass this request through, but I don't see one in a quick scan through the code.
The simplest workaround might be to instantiate a SAX parser yourself, configure it appropriately (don't forget to set "http://xml.org/sax/features/namespace-prefixes"; to true in addition to requesting a namespace-aware parser), make sure it has schema validation turned on, point it to the proper file, then wrap a SAXSource around it and pass that to Xalan. Not exactly elegant, and requires that you write a bit of code rather than calling Process.java, but this approach does let you do things we haven't yet exposed through our own controls.
