<book xlink:type="extended" xmlns:xlink="http://www.w3.org/1999/xlink">  <author>L. Frank Baum</author>  <title>The Wonderful Wizard of Oz</title>    <!-- locator elements -->  <edition xlink:type="locator" xlink:href="urn:isbn:0192839306"            xlink:title="Oxford University Press"            xlink:role="http://www.oup-usa.org/"            xlink:label="ISBN0192839306"/>     <store xlink:type="locator"          xlink:href="http://www.amazon.com/exec/obidos/ASIN/0192839306"         xlink:label="buy">Amazon</store>                    <store xlink:type="locator" xlink:href=    "http://www1.fatbrain.com/asp/bookinfo/bookinfo.asp?theisbn=0192839306"    xlink:label="buy">Fatbrain</store>                    <store xlink:type="locator" xlink:href="http://shop.bn.com/booksearch/isbninquiry.asp?isbn=0192839306"     xlink:label="buy">Barnes &amp; Noble</store>                    <!-- arcs -->  <purchase xlink:type="arc" xlink:from="ISBN0192839306" xlink:to="buy" /></book>