The DocBook DTD defines the structure of a DocBook
document. It contains rules about how the elements
may be used; and what the elements ought to be
describing. For example: it is the DocBook DTD
which states all warnings are to
warn the reader (this is the
definition of the element); and may not contain
plain text (this is the content model--and the
bit which forces you to wrap your warning text
in a para or perhaps a list).
It is important that you download the version(s) that match your document. You may want to configure your system now to deal with “all” DocBook DTDs if you are going to be editing older LDP documents. If you are a new author, you only need the first one listed: XML DTD for DocBook version 4.2.
The XML DTD is available from http://www.oasis-open.org/xml/4.2/. The LDP prefers this version of the DocBook DTD.
If you are going to be working with SGML versions of DocBook you will need one (or both) of: http://www.oasis-open.org/docbook/sgml/4.1/docbk41.zip or http://www.oasis-open.org/docbook/sgml/3.1/docbk31.zip
Example B.7. “Installing” DocBook Document Type Definitions
Create a base directory to store everything such as /opt/local/sgml/. Copy the DTDs
into a sub-directory named dtd.
The DocBook standard is described in these files. If you change these files, you are no longer working with DocBook.