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Daniel Veillardd2190fa2010-09-30 13:58:22 +0200[diff] [blame]1<?xml version="1.0" encoding="UTF-8"?>
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]10</style><title>Validation &amp; DTDs</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"><table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr><td width="120"><a href="http://swpat.ffii.org/"><img src="epatents.png" alt="Action against software patents" /></a></td><td width="180"><a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 Logo" /></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo" /></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo" /></a><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo" /></a></div></td><td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center"><h1>The XML C parser and toolkit of Gnome</h1><h2>Validation &amp; DTDs</h2></td></tr></table></td></tr></table></td></tr></table><table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr><td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr><tr><td bgcolor="#fffacd"><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="20" value="" /><input name="submit" type="submit" value="Search ..." /></form><ul><li><a href="index.html">Home</a></li><li><a href="html/index.html">Reference Manual</a></li><li><a href="intro.html">Introduction</a></li><li><a href="FAQ.html">FAQ</a></li><li><a href="docs.html" style="font-weight:bold">Developer Menu</a></li><li><a href="bugs.html">Reporting bugs and getting help</a></li><li><a href="help.html">How to help</a></li><li><a href="downloads.html">Downloads</a></li><li><a href="news.html">Releases</a></li><li><a href="XMLinfo.html">XML</a></li><li><a href="XSLT.html">XSLT</a></li><li><a href="xmldtd.html">Validation &amp; DTDs</a></li><li><a href="encoding.html">Encodings support</a></li><li><a href="catalog.html">Catalog support</a></li><li><a href="namespaces.html">Namespaces</a></li><li><a href="contribs.html">Contributions</a></li><li><a href="examples/index.html" style="font-weight:bold">Code Examples</a></li><li><a href="html/index.html" style="font-weight:bold">API Menu</a></li><li><a href="guidelines.html">XML Guidelines</a></li><li><a href="ChangeLog.html">Recent Changes</a></li></ul></td></tr></table><table width="100%" border="0" cellspacing="1" cellpadding="3"><tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr><tr><td bgcolor="#fffacd"><ul><li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li><li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li><li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li><li><a href="http://www.aleksey.com/xmlsec/">XML-DSig xmlsec</a></li><li><a href="ftp://xmlsoft.org/">FTP</a></li><li><a href="http://www.zlatkovic.com/projects/libxml/">Windows binaries</a></li><li><a href="http://opencsw.org/packages/libxml2">Solaris binaries</a></li><li><a href="http://www.explain.com.au/oss/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://lxml.de/">lxml Python bindings</a></li><li><a href="http://cpan.uwinnipeg.ca/dist/XML-LibXML">Perl bindings</a></li><li><a href="http://libxmlplusplus.sourceforge.net/">C++ bindings</a></li><li><a href="http://www.zend.com/php5/articles/php5-xmlphp.php#Heading4">PHP bindings</a></li><li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal bindings</a></li><li><a href="http://libxml.rubyforge.org/">Ruby bindings</a></li><li><a href="http://tclxml.sourceforge.net/">Tcl bindings</a></li><li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml2">Bug Tracker</a></li></ul></td></tr></table></td></tr></table></td><td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"><p>Table of Content:</p><ol>
11 <li><a href="#General5">General overview</a></li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]12 <li><a href="#definition">The definition</a></li>
Daniel Veillard1177ca42003-04-26 22:29:54 +0000[diff] [blame]13 <li><a href="#Simple">Simple rules</a>
Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]14 <ol>
15 <li><a href="#reference">How to reference a DTD from a document</a></li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]16 <li><a href="#Declaring">Declaring elements</a></li>
17 <li><a href="#Declaring1">Declaring attributes</a></li>
Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]18 </ol>
19 </li>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]20 <li><a href="#Some">Some examples</a></li>
21 <li><a href="#validate">How to validate</a></li>
22 <li><a href="#Other">Other resources</a></li>
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]23</ol><h3><a name="General5" id="General5">General overview</a></h3><p>Well what is validation and what is a DTD ?</p><p>DTD is the acronym for Document Type Definition. This is a description of
24the content for a family of XML files. This is part of the XML 1.0
25specification, and allows one to describe and verify that a given document
26instance conforms to the set of rules detailing its structure and content.</p><p>Validation is the process of checking a document against a DTD (more
27generally against a set of construction rules).</p><p>The validation process and building DTDs are the two most difficult parts
28of the XML life cycle. Briefly a DTD defines all the possible elements to be
29found within your document, what is the formal shape of your document tree
30(by defining the allowed content of an element; either text, a regular
31expression for the allowed list of children, or mixed content i.e. both text
32and children). The DTD also defines the valid attributes for all elements and
33the types of those attributes.</p><h3><a name="definition1" id="definition1">The definition</a></h3><p>The <a href="http://www.w3.org/TR/REC-xml">W3C XML Recommendation</a> (<a href="http://www.xml.com/axml/axml.html">Tim Bray's annotated version of
Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]34Rev1</a>):</p><ul>
35 <li><a href="http://www.w3.org/TR/REC-xml#elemdecls">Declaring
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]36 elements</a></li>
37 <li><a href="http://www.w3.org/TR/REC-xml#attdecls">Declaring
38 attributes</a></li>
39</ul><p>(unfortunately) all this is inherited from the SGML world, the syntax is
40ancient...</p><h3><a name="Simple1" id="Simple1">Simple rules</a></h3><p>Writing DTDs can be done in many ways. The rules to build them if you need
41something permanent or something which can evolve over time can be radically
42different. Really complex DTDs like DocBook ones are flexible but quite
43harder to design. I will just focus on DTDs for a formats with a fixed simple
44structure. It is just a set of basic rules, and definitely not exhaustive nor
45usable for complex DTD design.</p><h4><a name="reference1" id="reference1">How to reference a DTD from a document</a>:</h4><p>Assuming the top element of the document is <code>spec</code> and the dtd
46is placed in the file <code>mydtd</code> in the subdirectory
Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]47<code>dtds</code> of the directory from where the document were loaded:</p><p><code>&lt;!DOCTYPE spec SYSTEM "dtds/mydtd"&gt;</code></p><p>Notes:</p><ul>
48 <li>The system string is actually an URI-Reference (as defined in <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>) so you can use a
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]49 full URL string indicating the location of your DTD on the Web. This is a
50 really good thing to do if you want others to validate your document.</li>
51 <li>It is also possible to associate a <code>PUBLIC</code> identifier (a
52 magic string) so that the DTD is looked up in catalogs on the client side
53 without having to locate it on the web.</li>
54 <li>A DTD contains a set of element and attribute declarations, but they
55 don't define what the root of the document should be. This is explicitly
56 told to the parser/validator as the first element of the
57 <code>DOCTYPE</code> declaration.</li>
58</ul><h4><a name="Declaring2" id="Declaring2">Declaring elements</a>:</h4><p>The following declares an element <code>spec</code>:</p><p><code>&lt;!ELEMENT spec (front, body, back?)&gt;</code></p><p>It also expresses that the spec element contains one <code>front</code>,
59one <code>body</code> and one optional <code>back</code> children elements in
60this order. The declaration of one element of the structure and its content
61are done in a single declaration. Similarly the following declares
62<code>div1</code> elements:</p><p><code>&lt;!ELEMENT div1 (head, (p | list | note)*, div2?)&gt;</code></p><p>which means div1 contains one <code>head</code> then a series of optional
63<code>p</code>, <code>list</code>s and <code>note</code>s and then an
64optional <code>div2</code>. And last but not least an element can contain
65text:</p><p><code>&lt;!ELEMENT b (#PCDATA)&gt;</code></p><p><code>b</code> contains text or being of mixed content (text and elements
66in no particular order):</p><p><code>&lt;!ELEMENT p (#PCDATA|a|ul|b|i|em)*&gt;</code></p><p><code>p </code>can contain text or <code>a</code>, <code>ul</code>,
67<code>b</code>, <code>i </code>or <code>em</code> elements in no particular
68order.</p><h4><a name="Declaring1" id="Declaring1">Declaring attributes</a>:</h4><p>Again the attributes declaration includes their content definition:</p><p><code>&lt;!ATTLIST termdef name CDATA #IMPLIED&gt;</code></p><p>means that the element <code>termdef</code> can have a <code>name</code>
69attribute containing text (<code>CDATA</code>) and which is optional
70(<code>#IMPLIED</code>). The attribute value can also be defined within a
71set:</p><p><code>&lt;!ATTLIST list type (bullets|ordered|glossary)
72"ordered"&gt;</code></p><p>means <code>list</code> element have a <code>type</code> attribute with 3
73allowed values "bullets", "ordered" or "glossary" and which default to
74"ordered" if the attribute is not explicitly specified.</p><p>The content type of an attribute can be text (<code>CDATA</code>),
75anchor/reference/references
76(<code>ID</code>/<code>IDREF</code>/<code>IDREFS</code>), entity(ies)
77(<code>ENTITY</code>/<code>ENTITIES</code>) or name(s)
78(<code>NMTOKEN</code>/<code>NMTOKENS</code>). The following defines that a
79<code>chapter</code> element can have an optional <code>id</code> attribute
80of type <code>ID</code>, usable for reference from attribute of type
81IDREF:</p><p><code>&lt;!ATTLIST chapter id ID #IMPLIED&gt;</code></p><p>The last value of an attribute definition can be <code>#REQUIRED
82</code>meaning that the attribute has to be given, <code>#IMPLIED</code>
83meaning that it is optional, or the default value (possibly prefixed by
Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]84<code>#FIXED</code> if it is the only allowed).</p><p>Notes:</p><ul>
85 <li>Usually the attributes pertaining to a given element are declared in a
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]86 single expression, but it is just a convention adopted by a lot of DTD
87 writers:
Daniel Veillard64e73902000-11-24 13:28:38 +0000[diff] [blame]88 <pre>&lt;!ATTLIST termdef
89 id ID #REQUIRED
90 name CDATA #IMPLIED&gt;</pre>
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]91 <p>The previous construct defines both <code>id</code> and
92 <code>name</code> attributes for the element <code>termdef</code>.</p>
Daniel Veillard0b28e882002-07-24 23:47:05 +0000[diff] [blame]93 </li>
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]94</ul><h3><a name="Some1" id="Some1">Some examples</a></h3><p>The directory <code>test/valid/dtds/</code> in the libxml2 distribution
95contains some complex DTD examples. The example in the file
96<code>test/valid/dia.xml</code> shows an XML file where the simple DTD is
97directly included within the document.</p><h3><a name="validate1" id="validate1">How to validate</a></h3><p>The simplest way is to use the xmllint program included with libxml. The
98<code>--valid</code> option turns-on validation of the files given as input.
99For example the following validates a copy of the first revision of the XML
1001.0 specification:</p><p><code>xmllint --valid --noout test/valid/REC-xml-19980210.xml</code></p><p>the -- noout is used to disable output of the resulting tree.</p><p>The <code>--dtdvalid dtd</code> allows validation of the document(s)
101against a given DTD.</p><p>Libxml2 exports an API to handle DTDs and validation, check the <a href="http://xmlsoft.org/html/libxml-valid.html">associated
102description</a>.</p><h3><a name="Other1" id="Other1">Other resources</a></h3><p>DTDs are as old as SGML. So there may be a number of examples on-line, I
Daniel Veillarde38217a2013-05-10 15:40:13 +0800[diff] [blame]103will just list one for now, others pointers welcome:</p><ul>
104 <li><a href="http://www.xml101.com:8081/dtd/">XML-101 DTD</a></li>
Daniel Veillardf781dba2006-06-09 13:34:49 +0000[diff] [blame]105</ul><p>I suggest looking at the examples found under test/valid/dtd and any of
106the large number of books available on XML. The dia example in test/valid
107should be both simple and complete enough to allow you to build your own.</p><p></p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html>