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* AUTHORS: added William and Bjorn * include/libxml/*.h *.c README doc/*.html etc.: changed old email to daniel@veillard.com hopefully I won't have to do this again * doc/Makefile.am doc/html/*.html: cleanup makefile, checked that docs can be rebuilt cleanly now * include/libxml/xml*version.h*: removed include/libxml/xmlversion.h from CVs it's generated, added include/libxml/xmlwin32version.h also generated but which should change far less frequently. * catalog.c nanoftp.c: made sure to include libxml.h not libxml/xmlversion.h directly * include/libxml/*.h: include xmlwin32version.h instead of xmlversion.h when compiling on WIN32 and MSC Daniel
206 lines
7.8 KiB
HTML
206 lines
7.8 KiB
HTML
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<title>Libxml Input/Output handling</title>
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<meta name="GENERATOR" content="amaya V4.1">
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<meta http-equiv="Content-Type" content="text/html">
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<body bgcolor="#ffffff">
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<h1 align="center">Libxml DTD support</h1>
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<p>Location: <a
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href="http://xmlsoft.org/xmlio.html">http://xmlsoft.org/xmldtd.html</a></p>
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<p>Libxml home page: <a href="http://xmlsoft.org/">http://xmlsoft.org/</a></p>
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<p>Mailing-list archive: <a
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href="http://xmlsoft.org/messages/">http://xmlsoft.org/messages/</a></p>
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<p>Version: $Revision$</p>
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<p>Table of Content:</p>
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<ol>
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<li><a href="#General">General overview</a></li>
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<li><a href="#definition">The definition</a></li>
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<li><a href="#Simple">Simple rules</a>
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<ol>
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<li><a href="#reference">How to reference a DTD from a document</a></li>
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<li><a href="#Declaring">Declaring elements</a></li>
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<li><a href="#Declaring1">Declaring attributes</a></li>
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</ol>
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</li>
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<li><a href="#Some">Some examples</a></li>
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<li><a href="#validate">How to validate</a></li>
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<li><a href="#Other">Other resources</a></li>
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</ol>
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<h2><a name="General">General overview</a></h2>
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<p>DTD is the acronym for Document Type Definition. This is a description of
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the content for a familly of XML files. This is part of the XML 1.0
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specification, and alows to describe and check that a given document instance
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conforms to a set of rules detailing its structure and content.</p>
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<h2><a name="definition">The definition</a></h2>
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<p>The <a href="http://www.w3.org/TR/REC-xml">W3C XML Recommendation</a> (<a
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href="http://www.xml.com/axml/axml.html">Tim Bray's annotated version of
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Rev1</a>):</p>
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<ul>
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<li><a href="http://www.w3.org/TR/REC-xml#elemdecls">Declaring
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elements</a></li>
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<li><a href="http://www.w3.org/TR/REC-xml#attdecls">Declaring
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attributes</a></li>
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</ul>
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<p>(unfortunately) all this is inherited from the SGML world, the syntax is
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ancient...</p>
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<h2><a name="Simple">Simple rules</a></h2>
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<p>Writing DTD can be done in multiple ways, the rules to build them if you
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need something fixed or something which can evolve over time can be radically
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different. Really complex DTD like Docbook ones are flexible but quite harder
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to design. I will just focuse on DTDs for a formats with a fixed simple
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structure. It is just a set of basic rules, and definitely not exhaustive nor
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useable for complex DTD design.</p>
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<h3><a name="reference">How to reference a DTD from a document</a>:</h3>
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<p>Assuming the top element of the document is <code>spec</code> and the dtd
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is placed in the file <code>mydtd</code> in the subdirectory <code>dtds</code>
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of the directory from where the document were loaded:</p>
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<p><code><!DOCTYPE spec SYSTEM "dtds/mydtd"></code></p>
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<p>Notes:</p>
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<ul>
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<li>the system string is actually an URI-Reference (as defined in <a
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href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>) so you can use a
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full URL string indicating the location of your DTD on the Web, this is a
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really good thing to do if you want others to validate your document</li>
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<li>it is also possible to associate a <code>PUBLIC</code> identifier (a
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magic string) so that the DTd is looked up in catalogs on the client side
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without having to locate it on the web</li>
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<li>a dtd contains a set of elements and attributes declarations, but they
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don't define what the root of the document should be. This is explicitely
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told to the parser/validator as the first element of the
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<code>DOCTYPE</code> declaration.</li>
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</ul>
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<h3><a name="Declaring">Declaring elements</a>:</h3>
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<p>The following declares an element <code>spec</code>:</p>
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<p><code><!ELEMENT spec (front, body, back?)></code></p>
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<p>it also expresses that the spec element contains one <code>front</code>,
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one <code>body</code> and one optionnal <code>back</code> children elements in
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this order. The declaration of one element of the structure and its content
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are done in a single declaration. Similary the following declares
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<code>div1</code> elements:</p>
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<p><code><!ELEMENT div1 (head, (p | list | note)*, div2*)></code></p>
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<p>means div1 contains one <code>head</code> then a series of optional
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<code>p</code>, <code>list</code>s and <code>note</code>s and then an optional
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<code>div2</code>. And last but not least an element can contain text:</p>
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<p><code><!ELEMENT b (#PCDATA)></code></p>
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<p><code>b</code> contains text or being of mixed content (text and elements
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in no particular order):</p>
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<p><code><!ELEMENT p (#PCDATA|a|ul|b|i|em)*></code></p>
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<p><code>p </code>can contain text or <code>a</code>, <code>ul</code>,
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<code>b</code>, <code>i </code>or <code>em</code> elements in no particular
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order.</p>
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<h3><a name="Declaring1">Declaring attributes</a>:</h3>
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<p>again the attributes declaration includes their content definition:</p>
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<p><code><!ATTLIST termdef name CDATA #IMPLIED></code></p>
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<p>means that the element <code>termdef</code> can have a <code>name</code>
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attribute containing text (<code>CDATA</code>) and which is optionnal
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(<code>#IMPLIED</code>). The attribute value can also be defined within a
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set:</p>
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<p><code><!ATTLIST list type (bullets|ordered|glossary)
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"ordered"></code></p>
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<p>means <code>list</code> element have a <code>type</code> attribute with 3
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allowed values "bullets", "ordered" or "glossary" and which default to
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"ordered" if the attribute is not explicitely specified.</p>
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<p>The content type of an attribute can be text (<code>CDATA</code>),
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anchor/reference/references
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(<code>ID</code>/<code>IDREF</code>/<code>IDREFS</code>), entity(ies)
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(<code>ENTITY</code>/<code>ENTITIES</code>) or name(s)
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(<code>NMTOKEN</code>/<code>NMTOKENS</code>). The following defines that a
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<code>chapter</code> element can have an optional <code>id</code> attribute of
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type <code>ID</code>, usable for reference from attribute of type IDREF:</p>
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<p><code><!ATTLIST chapter id ID #IMPLIED></code></p>
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<p>The last value of an attribute definition can be <code>#REQUIRED
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</code>meaning that the attribute has to be given, <code>#IMPLIED</code>
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meaning that it is optional, or the default value (possibly prefixed by
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<code>#FIXED</code> if it is the only allowed).</p>
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<p>Notes:</p>
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<ul>
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<li>usually the attributes pertaining to a given element are declared in a
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single expression, but it is just a convention adopted by a lot of DTD
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writers:
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<pre><!ATTLIST termdef
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id ID #REQUIRED
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name CDATA #IMPLIED></pre>
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<p>The previous construct defines both <code>id</code> and
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<code>name</code> attributes for the element <code>termdef</code></p>
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</li>
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</ul>
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<h2><a name="Some">Some examples</a></h2>
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<p>The directory <code>test/valid/dtds/</code> in the libxml distribution
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contains some complex DTD examples. The <code>test/valid/dia.xml</code>
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example shows an XML file where the simple DTD is directly included within the
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document.</p>
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<h2><a name="validate">How to validate</a></h2>
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<p>The simplest is to use the xmllint program comming with libxml. The
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<code>--valid</code> option turn on validation of the files given as input,
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for example the following validates a copy of the first revision of the XML
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1.0 specification:</p>
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<p><code>xmllint --valid --noout test/valid/REC-xml-19980210.xml</code></p>
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<p>the -- noout is used to not output the resulting tree.</p>
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<p>The <code>--dtdvalid dtd</code> allows to validate the document(s) against
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a given DTD.</p>
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<p>Libxml exports an API to handle DTDs and validation, check the <a
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href="http://xmlsoft.org/html/libxml-valid.html">associated
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description</a>.</p>
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<h2><a name="Other">Other resources</a></h2>
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<p>DTDs are as old as SGML. So there may be a number of examples on-line, I
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will just list one for now, others pointers welcome:</p>
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<ul>
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<li><a href="http://www.xml101.com:8081/dtd/">XML-101 DTD</a></li>
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</ul>
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<p></p>
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<p><a href="mailto:daniel@veillard.com">Daniel Veillard</a></p>
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<p>$Id$</p>
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</body>
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</html>
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