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<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" /><link rel="SHORTCUT ICON" href="/favicon.ico" /><style type="text/css">TD {font-family: Verdana,Arial,Helvetica}BODY {font-family: Verdana,Arial,Helvetica; margin-top: 2em; margin-left: 0em; margin-right: 0em}H1 {font-family: Verdana,Arial,Helvetica}H2 {font-family: Verdana,Arial,Helvetica}H3 {font-family: Verdana,Arial,Helvetica}A:link, A:visited, A:active { text-decoration: underline }</style><title>Validation & 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 & 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" 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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://www.blastwave.org/packages.php/libxml2">Solaris binaries</a></li><li><a href="http://www.zveno.com/open_source/libxml2xslt.html">MacOsX binaries</a></li><li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal 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><li><a href="#General5">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><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 ofthe content for a family of XML files. This is part of the XML 1.0specification, and allows one to describe and verify that a given documentinstance conforms to the set of rules detailing its structure and content.</p><p>Validation is the process of checking a document against a DTD (moregenerally against a set of construction rules).</p><p>The validation process and building DTDs are the two most difficult partsof the XML life cycle. Briefly a DTD defines all the possible elements to befound within your document, what is the formal shape of your document tree(by defining the allowed content of an element; either text, a regularexpression for the allowed list of children, or mixed content i.e. both textand children). The DTD also defines the valid attributes for all elements andthe 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 ofRev1</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 isancient...</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 needsomething permanent or something which can evolve over time can be radicallydifferent. Really complex DTDs like DocBook ones are flexible but quiteharder to design. I will just focus on DTDs for a formats with a fixed simplestructure. It is just a set of basic rules, and definitely not exhaustive norusable 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 dtdis 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 element and attribute declarations, but they don't define what the root of the document should be. This is explicitly told to the parser/validator as the first element of the <code>DOCTYPE</code> declaration.</li></ul><h4><a name="Declaring2" id="Declaring2">Declaring elements</a>:</h4><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 optional <code>back</code> children elements inthis order. The declaration of one element of the structure and its contentare done in a single declaration. Similarly the following declares<code>div1</code> elements:</p><p><code><!ELEMENT div1 (head, (p | list | note)*, div2?)></code></p><p>which 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 anoptional <code>div2</code>. And last but not least an element can containtext:</p><p><code><!ELEMENT b (#PCDATA)></code></p><p><code>b</code> contains text or being of mixed content (text and elementsin 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 particularorder.</p><h4><a name="Declaring1" id="Declaring1">Declaring attributes</a>:</h4><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 optional(<code>#IMPLIED</code>). The attribute value can also be defined within aset:</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 3allowed values "bullets", "ordered" or "glossary" and which default to"ordered" if the attribute is not explicitly 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> attributeof type <code>ID</code>, usable for reference from attribute of typeIDREF:</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><h3><a name="Some1" id="Some1">Some examples</a></h3><p>The directory <code>test/valid/dtds/</code> in the libxml2 distributioncontains some complex DTD examples. The example in the file<code>test/valid/dia.xml</code> shows an XML file where the simple DTD isdirectly 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<code>--valid</code> option turns-on validation of the files given as input.For example the following validates a copy of the first revision of the XML1.0 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)against 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">associateddescription</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, Iwill 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>I suggest looking at the examples found under test/valid/dtd and any ofthe large number of books available on XML. The dia example in test/validshould 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>⌨️ 快捷键说明
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