DOCBOOK-APPS: XML declaration when validating

Here's another newbie question:

When using NTEmacs, is there a way to force the SGML Validate command to
insert the correct XML declaration for XML documents and the SGML
declaration for SGML documents? I'm tired of manually changing the command
line everytime I validate an XML document. It seems that sgml-declaration is
always used and never sgml-xml-declaration.

Can anyone help with this?

Thanks,
Dan