combining multiple data sources

I am looking for some suggestions on how to merge multiple sources of xml data
into a single stylesheet.  all of the sources will have an idnumber in common.
This example is simplified, and the id attribute doesn't necessarily have to be
in that position:

<Source1ML>
     <ADDRESS  id="100">
          <STREETNUM>123</STREETNUM>
          <STREETNAME>Main St.</STREETNAME>
     </ADDRESS>
</Source1ML>

<Source2ML>
     <CUSTOMER  id="100">
          <FIRSTNAME>John</FIRSTNAME>
          <MIDDLENAME>Q.</MIDDLENAME>
          <LASTNAME>Doe</LASTNAME>
     </CUSTOMER>
</Source2ML>

<Source3ML>
     <PHONENUMBER>
          <NPA>555</NPA>
          <NXX>555</NXX>
          <XXXX>1234</XXXX>
     </PHONENUMBER>
</Source3ML>

thanks.



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