JAXB( the XML databinding initiative from Sun ) makes use of DOM and promises to be more slightly more efficient. Since data binding involves making sure the objects are in-sync with the XML instance, it clearly leverages on DOM rather than SAX.
Any answer(s) to your question(s) will be a mere repitition of
JAXB Faq on Sun website, an excellent resource on XML databinding. The ambitious JAXPack initiative from Sun will include JAXB package among other goodies. I suggest that you checkout the documentation.
Cheers!
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Ajith Kallambella M. Sun Certified Programmer for the Java�2 Platform.
IBM Certified Developer - XML and Related Technologies, V1.
Co-author of
Java 2 Certification Passport