Database Software

I'm trying to using the variable operator (?) in an Oracle prepared statement used in a query where clause. Here is the query:

select xt.APPLICATION_NAME, xt.VERSION, xt.EVENT_TYPE, xt.SENDING_SITE, xt.RECEIVING_SITE, xt.EVENT_ID 
      from AUDITED_EVENT_XML_MIN e,
         XMLTable(XMLNAMESPACES('http://gov/va/med/datasharing/audit/endpoint/audit' AS "xae"),
                '/xae:auditable-event'
                PASSING e.xml_event_content
                COLUMNS
                APPLICATION_NAME VARCHAR2(255) PATH 'xae:application-name',
                VERSION          VARCHAR2(255) PATH 'xae:version',
                EVENT_TYPE       VARCHAR2(255) PATH 'xae:event-type',
                SENDING_SITE     VARCHAR2(255) PATH 'xae:xml-event-content/*/MSH/MSH.4/HD.2',
                RECEIVING_SITE   VARCHAR2(255) PATH 'xae:xml-event-content/*/MSH/MSH.6/HD.2',
                EVENT_ID         VARCHAR2(255) PATH 'xae:xml-event-content/*/MSH/MSH.10') xt
            where existsNode(E.XML_EVENT_CONTENT, '/xae:auditable-event[xae:event-type=?]','xmlns:xae="http://gov/va/med/datasharing/audit/endpoint/audit"') = 1

This code works when the ? is replaced with "aValue". I need to use the ? so that my Java client can pass a variable value into the query.
Is this a supportable feature or am I doing something wrong?
I didn't see any examples in the Oracle XML DB Developers Guide where there was a ? in an XPath expression.
I also tried "?" with the same issue...

Here is the version info:

SQL*Plus: Release 11.1.0.6.0 - Production on Mon Sep 10 18:41:55 2012

Copyright (c) 1982, 2007, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

Any assistance would be greatly appreciated.
Thanks in advance...

Edited by: flyeagle5683 on Sep 10, 2012 5:49 PM