Run the shell code below to put the DTD in Utilities/xml/docbook-4.5:
v=4.5 &&
sha1=b9124233b50668fb508773aa2b3ebc631d7c1620 &&
mkdir Utilities/xml/docbook-$v &&
cd Utilities/xml/docbook-$v &&
wget -c http://www.oasis-open.org/docbook/xml/$v/docbook-xml-$v.zip &&
sha1sum docbook-xml-$v.zip |grep $sha1 &&
unzip docbook-xml-$v.zip &&
rm docbook-xml-$v.zip
Brad King