DTD ID REF

Hi Guys,
         Thanks for the responses you have given. They were useful to me.

I have a DTD file in which I have element A which has two attributes with
IDREF properties. 
Now while creating xml file using DTD, how can I refer attribute IDREF
defined in another xml file?

<!ELEMNT A>
<!ATTLIST A B IDREF>
<!ATTLIST A C IDREF>

===================
first.xml
----------

<A B="x" C="y"/>


second.xml
-------------
<X ID="y">
.......
........
</X>

Any one had similar problems? or any input is appreciated!


Yours sincerely,
Bhaskar Yallala
DirectAdvice Inc,
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