<book>
<book:chapter id="bk444444ch1" type="CHAPTER">
<book:locator xlink:href="/book/isbn/979-0-4444-1000-17/book-part/chap
+ter/bk444444ch1?releaseStatus=RELEASED" xlink:title="Photonic crystal
+ light-emitting sources" xlink:type="locator" xmlns:xlink="http://www
+.w3.org/1999/xlink"/>
<book:locator xlink:href="/book/isbn/979-0-4444-1000-17/book-part/chap
+ter/bk444444ch1?releaseStatus=RELEASED&format=pdf" xlink:title="P
+hotonic crystal light-emitting sources" xlink:type="locator" xmlns:xl
+ink="http://www.w3.org/1999/xlink"/>
<book:locator xlink:href="/book/isbn/979-0-4444-1000-17/book-part/chap
+ter/bk444444ch1?releaseStatus=RELEASED&format=epub" xlink:title="
+Photonic crystal light-emitting sources" xlink:type="locator" xmlns:x
+link="http://www.w3.org/1999/xlink"/>
</book>
How can i get "xlink:href" of first instance of book:locator?