XSD with keys... what to use in Java to process XML?

If you've an XSD with key/keyref constraints, what is
the best XML parsing (JAXP vs JAXB) method to use in
Java?

I did some reading on this. I was inclined to use
Java-XML binding frameworks to leverage my XSD. But
JAXB 1.0 doesn't support key/keyref (meaning doesn't
support validation?? not sure).
Also not sure if JAXB 2.0 supports it.

OR should I use JAXP instead?

Parsing performance is not an issue for my
application.

  I know key/keyref constraints' use at the XSD
 level.
  Can you access these key/keyrefs at the Java
  application level?
  For e.g. I need to find the number of Keyrefs
  referencing the Key in my Java app?
  
  Basically, I am trying to understand if I can
  leverage these constraints at the Java level (like
  accessing selector/field values, xpath expressions,
  etc).
  
  Or are these constraints are only used at the XSD
  level and XML validation?
 
  In short, how would one leverage these key/keyrefs
 at the Java application level?
 
  Thanks for any pointers.


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