These are free software RPMs for working on and formatting DocBook documents on RedHat Linux.
DocBook XML Schema
This is a translation of the DocBook DTD into an XML Schema.
Get Going with DocBook
This is a nice tutorial that explains how to use DocBook.
What is DocBook?
An explanation of the XML language DocBook. A article discussing the design qualities and uses for DocBook that includes standard application and a general description of the XML language DocBook.