5.5. Naming and versioning DocBook customizations
DocBook V5.0 is not tightly coupled with some particular
validation technology like DTDs. This also means that DocBook V5.0
documents doesn't have to (and usually really doesn't) start with
document type declaration (<!DOCTYPE�>) which can specify schema
(DTD) to use. Instead, DocBook V5.0 instance can be easily
distinguished from other XML vocabularies by using elements in
http://docbook.org/ns/docbook namespace. This namespace is
enough to distinguish DocBook from other XML based formats. But
DocBook schema evolves over the time and there are several versions of
DocBook (e.g. 3.1, 4.2, 4.5 and 5.0). Since DocBook version 5.0 the
actual version used is indicated in the version attribute on a root element.
<book xmlns="http://docbook.org/ns/docbook"
version="5.0">
�
</book>
Future version of DocBook will start with the same markup, only
version number will be raised like 5.1 or 6.0. The namespace will remain
same until semantic of elements will change in a backward incompatible
way which is very unlikely to happen.
If you create DocBook schema customization you must change version attribute to distinguish your
customization from the �official� DocBook. Namespace
change is not recommended because it would break all processing
tools. Remember that changing namespace is the same as renaming all
elements in the namespace.
Your own version identifiers should use the following syntax in
order to record their DocBook derivation:
base_version [Subset|Extension|Variant]? [name [version]]+
For example:
5.0 Subset Simplified 1.0
5.0 Variant ASMBook
5.0 ASMBook 2006
5.0 Extension MathML 2.0 SVG 1.1
The first part of version identifier is a version number of the
DocBook schema from which you derived your customization.
If your schema is a proper subset, you can advertise this status
by using the Subset keyword in the description. If
your schema contains any markup model extensions, you can advertise
this status by using the Extension keyword. If
you'd rather not characterize your variant specifically as a subset or
an extension, you can leave out this field entirely, or, if you
prefer, use the Variant keyword.
After these keywords you can place whitespace separated list of
customization identifiers. Each name can be optionally followed by its
version number.