In the DocBook documentation for Boost for configuring local XSL and DTD distributions it says that the DocBook DTD is at the OASIS DocBook site at http://www.oasis-open.org/docbook/xml/4.2/index.shtml . However clicking this link gets a Resource not found message on the Oasis web site. However using http://www.oasis-open.org/docbook/xml/4.2 works for me, and http://www.oasis-open.org/docbook/xml/4.2/docbook-xml-4.2.zip is the actual zip file. Perhaps the document needs updating.