Norman Walsh, Sun Microsystems, Inc.
DocBook is general purpose [XML] schema particularly well suited to books and papers about computer hardware and software (though it is by no means limited to these applications).
The Version 5.0 release is a complete rewrite of DocBook in RELAX NG. The intent of this rewrite is to produce a schema that is true to the spirit of DocBook while simultaneously removing inconsistencies that have arisen as a natural consequence of DocBook's long, slow evolution. The Technical Committee has taken this opportunity to simplify a number of content models and tighten constraints where RELAX NG makes that possible.
The Technical Committee provides the DocBook 5.0 schema in other schema languages, including W3C XML Schema and an XML DTD, but the RELAX NG Schema is now the normative schema.
This Working Draft is an editor's draft. It does not necessarily represent the consensus of the committee.
The errata page for this specification is at http://docbook.org/specs/docbook-errata.html.
Copyright © 2001, 2002, 2003, 2004, 2005 The Organization for the Advancement of Structured Information Standards [OASIS]. All Rights Reserved.
DocBook is general purpose XML schema particularly well suited to books and papers about computer hardware and software (though it is by no means limited to these applications).
The DocBook Technical Committee maintains the DocBook schema. Starting with V5.0, DocBook is normatively available as a [RELAX NG] Schema. W3C XML Schema and Document Type Definition (DTD) versions are also available.
The Version 5.0 release is a complete rewrite. In programming-language terms, think of it as a code refactoring.
This rewrite introduces a large number of backwards-incompatible changes. Essentially all DocBook V4.x documents will have to be modified to validate against DocBook V5.0. An XSLT 1.0 stylesheet is provided to ease this transition.
The DocBook Technical Committee welcomes bug reports and requests for enhancement (RFEs) from the user community. The current list of outstanding requests is available through the SourceForge tracker interface. This is also the preferred mechanism for submitting new requests. Old RFEs, from a previous legacy tracking system, are archived for reference.
The key words must, must not, required, shall, shall not, should, should not, recommended, may, and optional in this Working Draft are to be interpreted as described in [RFC 2119]. Note that for reasons of style, these words are not capitalized in this document.
In V5.0, DocBook has been rewritten as a native RELAX NG grammar. The goals of this redesign were to produce a schema that:
“feels like” DocBook. Most existing documents should still be valid or it should be possible to transform them in simple, mechanical ways into valid documents.
enforces as many constraints as possible in the schema. Some additional constraints are expressed with Schematron rules.
cleans up the content models.
gives users the flexibility to extend or subset the schema in an easy and straightforward way.
can be used to generate XML DTD and W3C XML Schema versions of DocBook.
Under the ordinary operating rules of DocBook evolution, the only backwards incompatible changes that could be made in DocBook V5.0 were those announced in DocBook V4.0. In light of the fact that this is a complete rewrite, the Technical Committee gave itself the freedom to make "unannounced" backwards-incompatible changes for this one release.
A number of elements have been removed from DocBook. Many of these have been replaced by simpler, more versatile alternatives. Others have simply been removed because they are not believed to be widely used.
Table 1. DocBook Element Changes
Removed in favor of
Replaced by simpler
Replaced by ubiquitous linking, see Section 3.1.9, “Universal Linking”.
The content models of many inlines have been reduced, sometimes drastically. The parameter entity customization of DocBook V4.x and previous versions resulted in very broad content models for some inlines.
Consider, for example,
command in DocBook V4.4:
command ::= (#PCDATA|link|olink|ulink|action|application|classname|methodname| interfacename|exceptionname|ooclass|oointerface|ooexception| command|computeroutput|database|email|envar|errorcode|errorname| errortype|errortext|filename|function|guibutton|guiicon|guilabel| guimenu|guimenuitem|guisubmenu|hardware|interface|keycap|keycode| keycombo|keysym|literal|code|constant|markup|medialabel| menuchoice|mousebutton|option|optional|parameter|prompt|property| replaceable|returnvalue|sgmltag|structfield|structname|symbol| systemitem|uri|token|type|userinput|varname|nonterminal|anchor| remark|subscript|superscript|inlinegraphic|inlinemediaobject| indexterm|beginpage)*
In DocBook V5.0,
command has a much smaller, more rational content model:
command ::= * Zero or more of: o text o alt o anchor o annotation o biblioref o indexterm o inlinemediaobject o link o phrase o remark o replaceable o subscript o superscript o xref
DocBook V5.0 may be overzealous in its simplification of content models. The Technical Committee expects to adjust these simplifications during user testing. Users are encouraged to report places where formally valid documents can no longer be made valid because content models have been reduced.
DocBook V4.x has
sectioninfo, etc. DocBook would be smaller and simpler if it had a single
info element in all these places.
There’s an historical reason for the large number of unique names: customizers might very well want to adjust the content models of info elements at different levels. For example, a copyright statement might be required at the book level, or an an author forbidden at the sub-section level. In DTDs, there’s only one content model allowed per element name, so in order to support independent customization, each info element must have a different name.
In RELAX NG, no such limitation exists. We can use patterns to achieve both a single
info element while still allowing customizers to change its content model in different contexts. In light of this functionality, we've replaced all the various flavors of info with a single element name.
DocBook V5.0 enforces the constraint that titles are required on
articles and other large structures where they are effectively optional in DocBook V4.x. (They are optional only in the sense that DTDs are unable to enforce the constraint that they be present, the documentation has always made it clear that titles were required.)
In DocBook V4.x and earlier, the presence of a document type declaration served as a mechanism for identifying the DocBook version of a document. Although the declaration was not actually required, it was present in the vast majority of DocBook documents.
In RELAX NG, no similar declaration exists. Although a document type declaration might still be present, it seems likely that this will not usually be the case.
Nevertheless, downstream processors may benefit from some indication of the version of DocBook being used. As a result DocBook V5.0 adds a new
version attribute which must be present on the document element of a DocBook document.
Mixing versions is explicitly allowed and the version attribute may be used on other elements as well. This might be the case, for example, in a compound document constructed from multiple documents each with its own version.
DocBook V5.0 enforces attribute co-constraints such as the
otherclass attributes on
In DocBook V5.0, HTML tables and CALS tables are independently specified. Where the DTD of DocBook V4.x allows for incoherent mixing of the two models, DocBook V5.0 forbids such mixtures.
DocBook V5.0 adds a few simple data types. For example, the
cols attribute on
tgroup must be a positive integer.
Some of these constraints, such as the requirement that elements like
pubdate include a proper date-time type, may prove controversial. Users are encouraged to report places where formally valid documents can no longer be made valid because data types have been introduced.
Starting with DocBook V5.0, the
xlink:href attributes are available on almost all elements.
linkend attribute provides an ID/IDREF link within the document. The
xlink:href attribute provides a URI-based link.
ulink element has been removed from DocBook as URI-based links can now be achieved directly from the appropriate inline (such as
command). For instances where no specific semantic inline is needed,
link is still available. Where
link used to be limited to ID/IDREF linking, it now sports an
xlink:href attribute as well.
Support for extended links are provided through the
Accessibility is improved by allowing both inline and block annotations in most context. The
alt element is now allowed in most places for inline annotations, the new element
annotation supports block annotations.
The DocBook V4.x markup for Tables of Contents, or more generally for Lists of Titles, was complex and had not evolved quite in step with the rest of DocBook. In DocBook V5.0, it has all been replaced by a quite simple, recursive
While most Tables of Contents and Lists of Titles are generated automatically and authors never have to produce markup for them by hand, this simplified content model should make it easier for authors to generate when necessary. One possible application of hand-authored
toc markup is to generate custom hierarchies which can be assembled on-the-fly from a library of topics marked up in DocBook.
Grammar based validation technologies (like RELAX NG) and rule based validation technologies (like Schematron) are naturally complementary. Mixing them allows us to play to the strengths of each without stretching either to enforce constraints that they aren’t readily designed to enforce.
For example, DocBook NG requires that the root element of a document have an explicit version attribute. Because there are a great many elements that can be root elements in DocBook, and because they can almost all appear as descendants of a root element as well, it would be tedious to express this constraint in RELAX NG. But it is easy in a rule-based schema language.
DocBook V5.0 uses Schematron where appropriate.
From the very beginning, one of the goals of DocBook has been that users should be able to produce customizations that are either subsets of extensions of DocBook.
For users familiar with the intricacies of XML DTD syntax and the rather complex and highly stylized patterns of parameter entity usage in DocBook, this is possible in DocBook V4.x.
In DocBook V5.0, we hope to take advantage of RELAX NGs more robust design (and it's lack of pernicious determinism rules) to make customization easier.
Three schema design patterns get us most of the way there.
DocBook elements, particularly the inlines, can be divided into broad classes: general purpose, technical, error-related, operating-system related, bibliographic, publishing, etc. In DocBook V5.0, these are collected together in named patterns.
To add a new inline,
endpoint for example, to the list of technical inlines, one need only extend the appropriate pattern. If an element should appear in several classes, they can all be extended in the same way:
db.technical.inlines |= endpoint db.programming.inlines |= endpoint db.os.inlines |= endpoint
Much the same concept was used in DocBook V4.x, where instead of patterns we had parameter entities. However, the constraints of DTD validation severely limit the circumstances under which an element can appear twice in a content model. That meant that adding an element to one parameter entity might make it an error to add it to another. Such constraints do not exist in RELAX NG which greatly simplifies the customization.
Each element in DocBook V5.0 is defined by its own pattern. To change the content model of an element, only that pattern need be redefined. To remove an element from DocBook, that pattern can be redefined as "
There’s an XSLT 1.0 stylesheet for performing conversion from DocBook V4.x to DocBook V5.0. Presented with a valid DocBook V4.x document, it attempts to produce a valid DocBook V5.0 document.
It succeeds entirely automatically for the most part, though human intervention is suggested for constructs that might have multiple interpretations (and therefore multiple possible transformations).
Users are encouraged to report documents that are not successfully transformed by the stylesheet, especially those which do have valid DocBook V5.0 representations.
See http://www.relaxng.org/ for a list of tools that can validate an XML document using RELAX NG. Note that not all products are capable of evaluating the Schematron assertions in the schema.
This appendix registers a new MIME media type, "
This parameter has identical semantics to the
charset parameter of the
application/xml media type as specified in [RFC 3023] or its successors.
By virtue of DocBook XML content being XML, it has the same considerations when sent as "
application/docbook+xml" as does XML. See [RFC 3023], Section 3.2.
Several DocBook elements may refer to arbitrary URIs. In this case, the security issues of RFC 2396, section 7, should be considered.
This media type registration is for DocBook documents as described by [DocBook: TDG].
There is no experimental, vendor specific, or personal tree predecessor to "
application/docbook+xml", reflecting the fact that no applications currently recognize it. This new type is being registered in order to allow for the deployment of DocBook on the World Wide Web, as a first class XML application.
There is no single initial octet sequence that is always present in DocBook documents.
DocBook documents are most often identified with the extension ".xml".
The DocBook specification is a work product of the DocBook Technical Committee at OASIS.
For documents labeled as "
application/docbook+xml", the fragment identifier notation is exactly that for "
application/xml", as specified in [RFC 3023] or its successors.
The following individuals were members of the committee during the formulation of this Working Draft:
Steve Cogorno, Sun Microsystems
Gary Cornelius, Individual
Adam Di Carlo, Debian
Paul Grosso, Arbortext
Dick Hamilton, Hewlett-Packard
Nancy Harrison, IBM
Scott Hudson, Individual
Mark Johnson, Debian
Jirka Kosek, Individual
Larry Rowland, Hewlett-Packard
Michael Smith, Individual
Robert Stayton, Individual (Secretary)
Norman Walsh, Sun Microsystems (Chair, Editor)
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The limited permissions granted above are perpetual and will not be revoked by OASIS or its successors or assigns.
This document and the information contained herein is provided on an "AS IS" basis and OASIS DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
OASIS has been notified of intellectual property rights claimed in regard to some or all of the contents of this specification. For more information consult the online list of claimed rights.
For information on wether any patents have been disclosed that may be essential to implementing this specification, and any offers of patent licensing terms, please refer to the Intellectual Property Rights section of the DocBook web page (http://www.oasis-open.org/committees/docbook/)
[RELAX NG] James Clark, editor. RELAX NG Specification (Committee Specification). OASIS. 2001.
[XML] Tim Bray, Jean Paoli, C. M. Sperberg-McQueen, et. al., editors. Extensible Markup Language (XML) 1.0 (Third Edition). World Wide Web Consortium, 04 Feb 2004.
[XLink11] Steven DeRose, Eve Maler, David Orchard, Norman Walsh, editors. XML Linking Language (XLink) Version 1.1. World Wide Web Consortium, 2005.
[RFC 2119] IETF (Internet Engineering Task Force). RFC 2119: Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. 1997.
[RFC 3023] IETF (Internet Engineering Task Force). RFC 3023: XML Media Types. M. Murata, S. St. Laurent, D. Kohn. 2001.
[DocBook: TDG] Norman Walsh and Leonard Meullner. DocBook: The Definitive Guide. O’Reilly & Associates, 1999.
[SGML] JTC 1, SC 34. ISO 8879:1986 Information processing -- Text and office systems -- Standard Generalized Markup Language (SGML). 1986.
[W3C XML Schema] Henry S. Thompson, David Beech, Murray Maloney, et. al., editors. XML Schema Part 1: Structures. World Wide Web Consortium, 2000.
[W3C XML Datatypes] Paul V. Biron and Ashok Malhotra, editors. XML Schema Part 2: Datatypes. World Wide Web Consortium, 2000.
[Schematron] Rick Jelliffe, editor. The Schematron Assertion Language 1.5. Rick Jelliffe and Acedemia Sinica Computing Centre. 2001, 2001.