doc/xmldtd.html - platform/external/libxml2 - Gitiles

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 <h1 align="center">Libxml DTD support</h1>

 <p>Location: <a
 href="http://xmlsoft.org/xmlio.html">http://xmlsoft.org/xmldtd.html</a></p>

 <p>Libxml home page: <a href="http://xmlsoft.org/">http://xmlsoft.org/</a></p>

 <p>Mailing-list archive:  <a
 href="http://xmlsoft.org/messages/">http://xmlsoft.org/messages/</a></p>

 <p>Version: $Revision$</p>

 <p>Table of Content:</p>
 <ol>
   <li><a href="#General">General overview</a></li>
   <li><a href="#definition">The definition</a></li>
   <li><a href="#Simple">Simple rules</a>
     <ol>
       <li><a href="#reference">How to reference a DTD from a document</a></li>
       <li><a href="#Declaring">Declaring elements</a></li>
       <li><a href="#Declaring1">Declaring attributes</a></li>
     </ol>
   </li>
   <li><a href="#Some">Some examples</a></li>
   <li><a href="#validate">How to validate</a></li>
   <li><a href="#Other">Other resources</a></li>
 </ol>

 <h2><a name="General">General overview</a></h2>

 <p>DTD is the acronym for Document Type Definition. This is a description of
 the content for a familly of XML files. This is part of the XML 1.0
 specification, and alows to describe and check that a given document instance
 conforms to a set of rules detailing its structure and content.</p>

 <h2><a name="definition">The definition</a></h2>

 <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
 Rev1</a>):</p>
 <ul>
   <li><a href="http://www.w3.org/TR/REC-xml#elemdecls">Declaring
   elements</a></li>
   <li><a href="http://www.w3.org/TR/REC-xml#attdecls">Declaring
   attributes</a></li>
 </ul>

 <p>(unfortunately) all this is inherited from the SGML world, the syntax is
 ancient...</p>

 <h2><a name="Simple">Simple rules</a></h2>

 <p>Writing DTD can be done in multiple ways, the rules to build them if you
 need something fixed or something which can evolve over time can be radically
 different. Really complex DTD like Docbook ones are flexible but quite harder
 to design. I will just focuse on DTDs for a formats with a fixed simple
 structure. It is just a set of basic rules, and definitely not exhaustive nor
 useable for complex DTD design.</p>

 <h3><a name="reference">How to reference a DTD from a document</a>:</h3>

 <p>Assuming the top element of the document is <code>spec</code> and the dtd
 is placed in the file <code>mydtd</code> in the subdirectory <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>
   <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
     full URL string indicating the location of your DTD on the Web, this is a
     really good thing to do if you want others to validate your document</li>
   <li>it is also possible to associate a <code>PUBLIC</code> identifier (a
     magic string) so that the DTd is looked up in catalogs on the client side
     without having to locate it on the web</li>
   <li>a dtd contains a set of elements and attributes declarations, but they
     don't define what the root of the document should be. This is explicitely
     told to the parser/validator as the first element of the
     <code>DOCTYPE</code> declaration.</li>
 </ul>

 <h3><a name="Declaring">Declaring elements</a>:</h3>

 <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>,
 one <code>body</code> and one optionnal <code>back</code> children elements in
 this order. The declaration of one element of the structure and its content
 are done in a single declaration. Similary the following declares
 <code>div1</code> elements:</p>

 <p><code>&lt;!ELEMENT div1 (head, (p | list | note)*, div2*)&gt;</code></p>

 <p>means div1 contains one <code>head</code> then a series of optional
 <code>p</code>, <code>list</code>s and <code>note</code>s and then an optional
 <code>div2</code>. And last but not least an element can contain text:</p>

 <p><code>&lt;!ELEMENT b (#PCDATA)&gt;</code></p>

 <p><code>b</code> contains text or being of mixed content (text and elements
 in 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>,
 <code>b</code>, <code>i </code>or <code>em</code> elements in no particular
 order.</p>

 <h3><a name="Declaring1">Declaring attributes</a>:</h3>

 <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>
 attribute containing text (<code>CDATA</code>) and which is optionnal
 (<code>#IMPLIED</code>). The attribute value can also be defined within a
 set:</p>

 <p><code>&lt;!ATTLIST list type (bullets|ordered|glossary)
 "ordered"&gt;</code></p>

 <p>means <code>list</code> element have a <code>type</code> attribute with 3
 allowed values "bullets", "ordered" or "glossary" and which default to
 "ordered" if the attribute is not explicitely specified.</p>

 <p>The content type of an attribute can be text (<code>CDATA</code>),
 anchor/reference/references
 (<code>ID</code>/<code>IDREF</code>/<code>IDREFS</code>), entity(ies)
 (<code>ENTITY</code>/<code>ENTITIES</code>) or name(s)
 (<code>NMTOKEN</code>/<code>NMTOKENS</code>). The following defines that a
 <code>chapter</code> element can have an optional <code>id</code> attribute of
 type <code>ID</code>, usable for reference from attribute of type IDREF:</p>

 <p><code>&lt;!ATTLIST chapter id ID #IMPLIED&gt;</code></p>

 <p>The last value of an attribute definition can be <code>#REQUIRED
 </code>meaning that the attribute has to be given, <code>#IMPLIED</code>
 meaning that it is optional, or the default value (possibly prefixed by
 <code>#FIXED</code> if it is the only allowed).</p>

 <p>Notes:</p>
 <ul>
   <li>usually the attributes pertaining to a given element are declared in a
     single expression, but it is just a convention adopted by a lot of DTD
     writers:
     <pre>&lt;!ATTLIST termdef
           id      ID      #REQUIRED
           name    CDATA   #IMPLIED&gt;</pre>
     <p>The previous construct defines both <code>id</code> and
     <code>name</code> attributes for the element <code>termdef</code></p>
   </li>
 </ul>

 <h2><a name="Some">Some examples</a></h2>

 <p>The directory <code>test/valid/dtds/</code> in the libxml distribution
 contains some complex DTD examples. The  <code>test/valid/dia.xml</code>
 example shows an XML file where the simple DTD is directly included within the
 document.</p>

 <h2><a name="validate">How to validate</a></h2>

 <p>The simplest is to use the xmllint program comming with libxml. The
 <code>--valid</code> option turn on validation of the files given as input,
 for example the following validates a copy of the first revision of the XML
 1.0 specification:</p>

 <p><code>xmllint --valid --noout test/valid/REC-xml-19980210.xml</code></p>

 <p>the -- noout is used to not output the resulting tree.</p>

 <p>The <code>--dtdvalid dtd</code> allows to validate the document(s) against
 a given DTD.</p>

 <p>Libxml exports an API to handle DTDs and validation, check the <a
 href="http://xmlsoft.org/html/libxml-valid.html">associated
 description</a>.</p>

 <h2><a name="Other">Other resources</a></h2>

 <p>DTDs are as old as SGML. So there may be a number of examples on-line, I
 will just list one for now, others pointers welcome:</p>
 <ul>
   <li><a href="http://www.xml101.com:8081/dtd/">XML-101 DTD</a></li>
 </ul>

 <p></p>

 <p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>

 <p>$Id$</p>
 </body>
 </html>
	<html>
	<head>
	<title>Libxml Input/Output handling</title>
	<meta name="GENERATOR" content="amaya V4.1">
	<meta http-equiv="Content-Type" content="text/html">
	</head>

	<body bgcolor="#ffffff">
	<h1 align="center">Libxml DTD support</h1>

	<p>Location: <a
	href="http://xmlsoft.org/xmlio.html">http://xmlsoft.org/xmldtd.html</a></p>

	<p>Libxml home page: <a href="http://xmlsoft.org/">http://xmlsoft.org/</a></p>

	<p>Mailing-list archive: <a
	href="http://xmlsoft.org/messages/">http://xmlsoft.org/messages/</a></p>

	<p>Version: $Revision$</p>

	<p>Table of Content:</p>
	<ol>
	<li><a href="#General">General overview</a></li>
	<li><a href="#definition">The definition</a></li>
	<li><a href="#Simple">Simple rules</a>
	<ol>
	<li><a href="#reference">How to reference a DTD from a document</a></li>
	<li><a href="#Declaring">Declaring elements</a></li>
	<li><a href="#Declaring1">Declaring attributes</a></li>
	</ol>
	</li>
	<li><a href="#Some">Some examples</a></li>
	<li><a href="#validate">How to validate</a></li>
	<li><a href="#Other">Other resources</a></li>
	</ol>

	<h2><a name="General">General overview</a></h2>

	<p>DTD is the acronym for Document Type Definition. This is a description of
	the content for a familly of XML files. This is part of the XML 1.0
	specification, and alows to describe and check that a given document instance
	conforms to a set of rules detailing its structure and content.</p>

	<h2><a name="definition">The definition</a></h2>

	<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
	Rev1</a>):</p>
	<ul>
	<li><a href="http://www.w3.org/TR/REC-xml#elemdecls">Declaring
	elements</a></li>
	<li><a href="http://www.w3.org/TR/REC-xml#attdecls">Declaring
	attributes</a></li>
	</ul>

	<p>(unfortunately) all this is inherited from the SGML world, the syntax is
	ancient...</p>

	<h2><a name="Simple">Simple rules</a></h2>

	<p>Writing DTD can be done in multiple ways, the rules to build them if you
	need something fixed or something which can evolve over time can be radically
	different. Really complex DTD like Docbook ones are flexible but quite harder
	to design. I will just focuse on DTDs for a formats with a fixed simple
	structure. It is just a set of basic rules, and definitely not exhaustive nor
	useable for complex DTD design.</p>

	<h3><a name="reference">How to reference a DTD from a document</a>:</h3>

	<p>Assuming the top element of the document is <code>spec</code> and the dtd
	is placed in the file <code>mydtd</code> in the subdirectory <code>dtds</code>
	of the directory from where the document were loaded:</p>

	<p><code><!DOCTYPE spec SYSTEM "dtds/mydtd"></code></p>

	<p>Notes:</p>
	<ul>
	<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
	full URL string indicating the location of your DTD on the Web, this is a
	really good thing to do if you want others to validate your document</li>
	<li>it is also possible to associate a <code>PUBLIC</code> identifier (a
	magic string) so that the DTd is looked up in catalogs on the client side
	without having to locate it on the web</li>
	<li>a dtd contains a set of elements and attributes declarations, but they
	don't define what the root of the document should be. This is explicitely
	told to the parser/validator as the first element of the
	<code>DOCTYPE</code> declaration.</li>
	</ul>

	<h3><a name="Declaring">Declaring elements</a>:</h3>

	<p>The following declares an element <code>spec</code>:</p>

	<p><code><!ELEMENT spec (front, body, back?)></code></p>

	<p>it also expresses that the spec element contains one <code>front</code>,
	one <code>body</code> and one optionnal <code>back</code> children elements in
	this order. The declaration of one element of the structure and its content
	are done in a single declaration. Similary the following declares
	<code>div1</code> elements:</p>

	<p><code><!ELEMENT div1 (head, (p \| list \| note), div2)></code></p>

	<p>means div1 contains one <code>head</code> then a series of optional
	<code>p</code>, <code>list</code>s and <code>note</code>s and then an optional
	<code>div2</code>. And last but not least an element can contain text:</p>

	<p><code><!ELEMENT b (#PCDATA)></code></p>

	<p><code>b</code> contains text or being of mixed content (text and elements
	in no particular order):</p>

	<p><code><!ELEMENT p (#PCDATA\|a\|ul\|b\|i\|em)*></code></p>

	<p><code>p </code>can contain text or <code>a</code>, <code>ul</code>,
	<code>b</code>, <code>i </code>or <code>em</code> elements in no particular
	order.</p>

	<h3><a name="Declaring1">Declaring attributes</a>:</h3>

	<p>again the attributes declaration includes their content definition:</p>

	<p><code><!ATTLIST termdef name CDATA #IMPLIED></code></p>

	<p>means that the element <code>termdef</code> can have a <code>name</code>
	attribute containing text (<code>CDATA</code>) and which is optionnal
	(<code>#IMPLIED</code>). The attribute value can also be defined within a
	set:</p>

	<p><code><!ATTLIST list type (bullets\|ordered\|glossary)
	"ordered"></code></p>

	<p>means <code>list</code> element have a <code>type</code> attribute with 3
	allowed values "bullets", "ordered" or "glossary" and which default to
	"ordered" if the attribute is not explicitely specified.</p>

	<p>The content type of an attribute can be text (<code>CDATA</code>),
	anchor/reference/references
	(<code>ID</code>/<code>IDREF</code>/<code>IDREFS</code>), entity(ies)
	(<code>ENTITY</code>/<code>ENTITIES</code>) or name(s)
	(<code>NMTOKEN</code>/<code>NMTOKENS</code>). The following defines that a
	<code>chapter</code> element can have an optional <code>id</code> attribute of
	type <code>ID</code>, usable for reference from attribute of type IDREF:</p>

	<p><code><!ATTLIST chapter id ID #IMPLIED></code></p>

	<p>The last value of an attribute definition can be <code>#REQUIRED
	</code>meaning that the attribute has to be given, <code>#IMPLIED</code>
	meaning that it is optional, or the default value (possibly prefixed by
	<code>#FIXED</code> if it is the only allowed).</p>

	<p>Notes:</p>
	<ul>
	<li>usually the attributes pertaining to a given element are declared in a
	single expression, but it is just a convention adopted by a lot of DTD
	writers:
	<pre><!ATTLIST termdef
	id ID #REQUIRED
	name CDATA #IMPLIED></pre>
	<p>The previous construct defines both <code>id</code> and
	<code>name</code> attributes for the element <code>termdef</code></p>
	</li>
	</ul>

	<h2><a name="Some">Some examples</a></h2>

	<p>The directory <code>test/valid/dtds/</code> in the libxml distribution
	contains some complex DTD examples. The <code>test/valid/dia.xml</code>
	example shows an XML file where the simple DTD is directly included within the
	document.</p>

	<h2><a name="validate">How to validate</a></h2>

	<p>The simplest is to use the xmllint program comming with libxml. The
	<code>--valid</code> option turn on validation of the files given as input,
	for example the following validates a copy of the first revision of the XML
	1.0 specification:</p>

	<p><code>xmllint --valid --noout test/valid/REC-xml-19980210.xml</code></p>

	<p>the -- noout is used to not output the resulting tree.</p>

	<p>The <code>--dtdvalid dtd</code> allows to validate the document(s) against
	a given DTD.</p>

	<p>Libxml exports an API to handle DTDs and validation, check the <a
	href="http://xmlsoft.org/html/libxml-valid.html">associated
	description</a>.</p>

	<h2><a name="Other">Other resources</a></h2>

	<p>DTDs are as old as SGML. So there may be a number of examples on-line, I
	will just list one for now, others pointers welcome:</p>
	<ul>
	<li><a href="http://www.xml101.com:8081/dtd/">XML-101 DTD</a></li>
	</ul>

	<p></p>

	<p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>

	<p>$Id$</p>
	</body>
	</html>