Difficulty in retrieving structured information from an XML file into an Ant Script

[Mast]

We would like to record project metadata in an XML Schema document.
Elements within this metadata document need to reference information
stored in other elements, and we are trying to define such
relationships through IDREF relationships.

I am unable to find a way to define the schema to retrieve information
through an IDREF relationship from the project metadata file. For
example, I need to define the schema for the following XML document
where the attributes, sub-elements or value of the <a id="x1"> element
that is referenced through the sub-element <a refid="x1"> of the <x>
element of the following xml document:

Ant does this using path id and refid task. Since I am using my custom
schema for metadata I cannot use this task anymore. I would like the
ant to read my schema conformant XML.
I am new to XML and trying to use JBuilderX and Ant1.6.5.

<project>
<x><a refid="x1"/></x>
<a id="x1" attr1="abc">
<description>ABC - This is element X1 description</description>
</a>
<a id="x2" attr1="xyz">
<description>XYZ - This is element X2 description</description>
</a>
</project>

I someone post the schema for above XML it would be great help.