Gitiles
Code Review Sign In
gerrit-public.fairphone.software / platform / external / libxml2 / 402e8c88652719c0fe74d6a8d4382b716a62d68b / . / doc / xml.html
blob: 395ae110a9468a5b3a0a5318460fec2d7de79669 [file] [log] [blame]
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]2 "http://www.w3.org/TR/REC-html40/loose.dtd">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]3<html>
4<head>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]5 <title>The XML library for Gnome</title>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]6 <meta name="GENERATOR" content="amaya V2.4">
7 <meta http-equiv="Content-Type" content="text/html">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]8</head>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]9
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]10<body bgcolor="#ffffff">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]11<h1 align="center">The XML library for Gnome</h1>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]12
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]13<h2 style="text-align: center">libxml, a.k.a. gnome-xml</h2>
14
15<p></p>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]16<ul>
17 <li><a href="#Introducti">Introduction</a></li>
18 <li><a href="#Documentat">Documentation</a></li>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]19 <li><a href="#Downloads">Downloads</a></li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]20 <li><a href="#News">News</a></li>
21 <li><a href="#XML">XML</a></li>
22 <li><a href="#tree">The tree output</a></li>
23 <li><a href="#interface">The SAX interface</a></li>
24 <li><a href="#library">The XML library interfaces</a>
25 <ul>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]26 <li><a href="#Invoking">Invoking the parser: the pull way</a></li>
27 <li><a href="#Invoking">Invoking the parser: the push way</a></li>
28 <li><a href="#Invoking2">Invoking the parser: the SAX interface</a></li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]29 <li><a href="#Building">Building a tree from scratch</a></li>
30 <li><a href="#Traversing">Traversing the tree</a></li>
31 <li><a href="#Modifying">Modifying the tree</a></li>
32 <li><a href="#Saving">Saving the tree</a></li>
33 <li><a href="#Compressio">Compression</a></li>
34 </ul>
35 </li>
36 <li><a href="#Entities">Entities or no entities</a></li>
37 <li><a href="#Namespaces">Namespaces</a></li>
38 <li><a href="#Validation">Validation</a></li>
39 <li><a href="#Principles">DOM principles</a></li>
40 <li><a href="#real">A real example</a></li>
41</ul>
42
43<h2><a name="Introducti">Introduction</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]44
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]45<p>This document describes libxml, the <a href="http://www.w3.org/XML/">XML</a>
46library provided in the <a href="http://www.gnome.org/">Gnome</a> framework.
47XML is a standard for building tag-based structured documents/data.</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]48
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]49<p>Here are some key points about libxml:</p>
50<ul>
51 <li>The internal document repesentation is as close as possible to the <a
52 href="http://www.w3.org/DOM/">DOM</a> interfaces.</li>
53 <li>Libxml also has a <a href="http://www.megginson.com/SAX/index.html">SAX
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]54 like interface</a>; the interface is designed to be compatible with <a
55 href="http://www.jclark.com/xml/expat.html">Expat</a>.</li>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]56 <li>Libxml now include a nearly complete <a
57 href="http://www.w3.org/TR/xpath">XPath</a> implementation.</li>
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]58 <li>Libxml exports Push and Pull type parser interfaces for both XML and
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]59 HTML.</li>
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]60 <li>This library is released both under the W3C Copyright and the GNU LGPL.
61 Basically, everybody should be happy; if not, drop me a mail.</li>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]62</ul>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]63
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]64<h2><a name="Documentat">Documentation</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]65
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]66<p>There are some on-line resources about using libxml:</p>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]67<ol>
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]68 <li>The code is commented in a way which allows <a
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]69 href="http://xmlsoft.org/libxml.html">extensive documentation</a> to be
70 automatically extracted.</li>
71 <li>This page provides a global overview and <a href="#real">some
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]72 examples</a> on how to use libxml.</li>
73 <li><a href="mailto:james@daa.com.au">James Henstridge</a> wrote <a
74 href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">some nice
75 documentation</a> explaining how to use the libxml SAX interface.</li>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]76 <li>George Lebl wrote <a
77 href="http://www-4.ibm.com/software/developer/library/gnome3/">an article
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]78 for IBM developerWorks</a> about using libxml.</li>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]79 <li>It is also a good idea to check to <a href="mailto:raph@levien.com">Raph
80 Levien</a> <a href="http://levien.com/gnome/">web site</a> since he is
81 building the <a href="http://levien.com/gnome/gdome.html">DOM interface
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]82 gdome</a> on top of libxml result tree and an implementation of <a
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]83 href="http://www.w3.org/Graphics/SVG/">SVG</a> called <a
84 href="http://www.levien.com/svg/">gill</a>. Check his <a
85 href="http://www.levien.com/gnome/domination.html">DOMination
86 paper</a>.</li>
87 <li>And don't forget to look at the <a href="/messages/">mailing-list
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]88 archive</a>, too.</li>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]89</ol>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]90
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]91<h3>Reporting bugs and getting help</h3>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]92
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]93<p>Well, bugs or missing features are always possible, and I will make a point
94of fixing them in a timely fashion. The best way to report a bug is to <a
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]95href="http://bugs.gnome.org/db/pa/lgnome-xml.html">use the Gnome bug tracking
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]96database</a>. I look at reports there regularly and it's good to have a
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]97reminder when a bug is still open. Check the <a
98href="http://bugs.gnome.org/Reporting.html">instructions on reporting bugs</a>
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]99and be sure to specify that the bug is for the package gnome-xml.</p>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]100
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]101<p>There is also a mailing-list <a
102href="mailto:xml@rufus.w3.org">xml@rufus.w3.org</a> for libxml, with an <a
103href="http://xmlsoft.org/messages">on-line archive</a>. To subscribe to this
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]104majordomo based list, send a mail message to <a
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]105href="mailto:majordomo@rufus.w3.org">majordomo@rufus.w3.org</a> with
106"subscribe xml" in the <strong>content</strong> of the message.</p>
107
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]108<p>Alternatively, you can just send the bug to the <a
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]109href="mailto:xml@rufus.w3.org">xml@rufus.w3.org</a> list.</p>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]110
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]111<h2><a name="Downloads">Downloads</a></h2>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]112
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]113<p>Latest versions can be found on <a
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]114href="ftp://rpmfind.net/pub/veillard/">rpmfind.net</a> or on the <a
115href="ftp://ftp.gnome.org/pub/GNOME/MIRRORS.html">Gnome FTP server</a> either
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]116as a <a href="ftp://ftp.gnome.org/pub/GNOME/stable/sources/libxml/">source
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]117archive</a> or <a href="ftp://ftp.gnome.org/pub/GNOME/contrib/rpms/">RPMs
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]118packages</a> (NOTE that you need both the <a
119href="http://rpmfind.net/linux/RPM/libxml.html">libxml</a> and <a
120href="http://rpmfind.net/linux/RPM/libxml-devel.html">libxml-devel</a>
121packages installed to compile applications using libxml).</p>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]122
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]123<p>Libxml is also available from 2 CVS bases:</p>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]124<ul>
125 <li><p>The <a href="http://dev.w3.org/cvsweb/XML/">W3C CVS base</a>,
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]126 available read-only using the CVS pserver authentification (I tend to use
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]127 this base for my own development, so it's updated more regularly, but
128 the content may not be as stable):</p>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]129 <pre>CVSROOT=:pserver:anonymous@dev.w3.org:/sources/public
130password: anonymous
131module: XML</pre>
132 </li>
133 <li><p>The <a
134 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&amp;dir=gnome-xml">Gnome
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]135 CVS base</a>. Check the <a
136 href="http://developer.gnome.org/tools/cvs.html">Gnome CVS Tools</a> page;
137 the CVS module is <b>gnome-xml</b>.</p>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]138 </li>
139</ul>
140
141<h2><a name="News">News</a></h2>
142
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]143<h3>CVS only : check the <a
144href="http://cvs.gnome.org/lxr/source/gnome-xml/ChangeLog">Changelog</a> file
145for really accurate description</h3>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]146<ul>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]147 <li>working on HTML and XML links recognition layers, get in touch with me
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]148 if you want to test those.</li>
Daniel Veillardda07c342000-01-25 18:31:22 +0000[diff] [blame]149 <li>there is some kind of roadmap to libxml-2.0: fix I18N, and <a
150 href="http://rpmfind.net/tools/gdome/messages/0039.html">change structures
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]151 to accommodate DOM</a></li>
Daniel Veillarde41f2b72000-01-30 20:00:07 +0000[diff] [blame]152</ul>
153
154<h3>1.8.6: Jan 31 2000</h3>
155<ul>
156 <li>added a nanoFTP transport module, debugged until the new version of <a
157 href="http://rpmfind.net/linux/rpm2html/rpmfind.html">rpmfind</a> can use
158 it without troubles</li>
Daniel Veillardda07c342000-01-25 18:31:22 +0000[diff] [blame]159</ul>
160
161<h3>1.8.5: Jan 21 2000</h3>
162<ul>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]163 <li>adding APIs to parse a well balanced chunk of XML (production <a
164 href="http://www.w3.org/TR/REC-xml#NT-content">[43] content</a> of the XML
165 spec)</li>
Daniel Veillard461a66c2000-01-18 18:01:01 +0000[diff] [blame]166 <li>fixed a hideous bug in xmlGetProp pointed by Rune.Djurhuus@fast.no</li>
167 <li>Jody Goldberg &lt;jgoldberg@home.com> provided another patch trying to
168 solve the zlib checks problems</li>
169 <li>The current state in gnome CVS base is expected to ship as 1.8.5 with
170 gnumeric soon</li>
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]171</ul>
172
173<h3>1.8.4: Jan 13 2000</h3>
174<ul>
175 <li>bug fixes, reintroduced xmlNewGlobalNs(), fixed xmlNewNs()</li>
176 <li>all exit() call should have been removed from libxml</li>
177 <li>fixed a problem with INCLUDE_WINSOCK on WIN32 platform</li>
178 <li>added newDocFragment()</li>
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]179</ul>
180
181<h3>1.8.3: Jan 5 2000</h3>
182<ul>
183 <li>a Push interface for the XML and HTML parsers</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]184 <li>an shell like interface to the document tree (try tester --shell
185 :-)</li>
Daniel Veillarddbfd6411999-12-28 16:35:14 +0000[diff] [blame]186 <li>lots of bug fixes and improvement added over XMas hollidays</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]187 <li>fixed the DTD parsing code to work with the xhtml DTD</li>
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]188 <li>added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()</li>
189 <li>Fixed bugs in xmlNewNs()</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]190 <li>External entity loading code has been revamped, now it uses
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame]191 xmlLoadExternalEntity(), some fix on entities processing were added</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]192 <li>cleaned up WIN32 includes of socket stuff</li>
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]193</ul>
194
195<h3>1.8.2: Dec 21 1999</h3>
196<ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]197 <li>I got another problem with includes and C++, I hope this issue is fixed
198 for good this time</li>
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]199 <li>Added a few tree modification functions: xmlReplaceNode,
200 xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and
201 xmlDocSetRootElement</li>
202 <li>Tried to improve the HTML output with help from <a
203 href="mailto:clahey@umich.edu">Chris Lahey</a></li>
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]204</ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]205
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]206<h3>1.8.1: Dec 18 1999</h3>
207<ul>
208 <li>various patches to avoid troubles when using libxml with C++ compilers
209 the "namespace" keyword and C escaping in include files</li>
210 <li>a problem in one of the core macros IS_CHAR was corrected</li>
211 <li>fixed a bug introduced in 1.8.0 breaking default namespace processing,
212 and more specifically the Dia application</li>
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]213 <li>fixed a posteriori validation (validation after parsing, or by using a
214 Dtd not specified in the original document)</li>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]215 <li>fixed a bug in</li>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]216</ul>
217
218<h3>1.8.0: Dec 12 1999</h3>
219<ul>
220 <li>cleanup, especially memory wise</li>
221 <li>the parser should be more reliable, especially the HTML one, it should
222 not crash, whatever the input !</li>
223 <li>Integrated various patches, especially a speedup improvement for large
224 dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>,
225 configure with --with-buffers to enable them.</li>
226 <li>attribute normalization, oops should have been added long ago !</li>
227 <li>attributes defaulted from Dtds should be available, xmlSetProp() now
228 does entities escapting by default.</li>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]229</ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]230
231<h3>1.7.4: Oct 25 1999</h3>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]232<ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]233 <li>Lots of HTML improvement</li>
234 <li>Fixed some errors when saving both XML and HTML</li>
235 <li>More examples, the regression tests should now look clean</li>
236 <li>Fixed a bug with contiguous charref</li>
237</ul>
238
239<h3>1.7.3: Sep 29 1999</h3>
240<ul>
241 <li>portability problems fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]242 <li>snprintf was used unconditionnally, leading to link problems on system
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]243 were it's not available, fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]244</ul>
245
246<h3>1.7.1: Sep 24 1999</h3>
247<ul>
248 <li>The basic type for strings manipulated by libxml has been renamed in
249 1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason
250 is that CHAR was conflicting with a predefined type on Windows. However on
251 non WIN32 environment, compatibility is provided by the way of a
252 <strong>#define </strong>.</li>
253 <li>Changed another error : the use of a structure field called errno, and
254 leading to troubles on platforms where it's a macro</li>
255</ul>
256
257<h3>1.7.0: sep 23 1999</h3>
258<ul>
259 <li>Added the ability to fetch remote DTD or parsed entities, see the <a
260 href="gnome-xml-nanohttp.html">nanohttp</a> module.</li>
261 <li>Added an errno to report errors by another mean than a simple printf
262 like callback</li>
263 <li>Finished ID/IDREF support and checking when validation</li>
264 <li>Serious memory leaks fixed (there is now a <a
265 href="gnome-xml-xmlmemory.html">memory wrapper</a> module)</li>
266 <li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a>
267 implementation</li>
268 <li>Added an HTML parser front-end</li>
269</ul>
270
271<h2><a name="XML">XML</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]272
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]273<p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for
274markup-based structured documents. Here is <a name="example">an example
275XML document</a>:</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]276<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]277&lt;EXAMPLE prop1="gnome is great" prop2="&amp;amp; linux too">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]278 &lt;head>
279 &lt;title>Welcome to Gnome&lt;/title>
280 &lt;/head>
281 &lt;chapter>
282 &lt;title>The Linux adventure&lt;/title>
283 &lt;p>bla bla bla ...&lt;/p>
284 &lt;image href="linus.gif"/>
285 &lt;p>...&lt;/p>
286 &lt;/chapter>
287&lt;/EXAMPLE></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]288
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]289<p>The first line specifies that it's an XML document and gives useful
290information about its encoding. Then the document is a text format whose
291structure is specified by tags between brackets. <strong>Each tag opened has
292to be closed</strong>. XML is pedantic about this. However, if a tag is
293empty (no content), a single tag can serve as both the opening and closing
294tag if it ends with <code>/></code> rather than with <code>></code>.
295Note that, for example, the
296image tag has no content (just an attribute) and is closed by ending the
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]297tag with <code>/></code>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]298
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]299<p>XML can be applied sucessfully to a wide range of uses, from long term
300structured document maintenance (where it follows the steps of SGML) to simple
301data encoding mechanisms like configuration file formatting (glade), spreadsheets
302(gnumeric), or even shorter lived documents such as WebDAV where it is used to
303encode remote calls between a client and a server.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]304
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]305<h2><a name="tree">The tree output</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]306
307<p>The parser returns a tree built during the document analysis. The value
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]308returned is an <strong>xmlDocPtr</strong> (i.e., a pointer to an
309<strong>xmlDoc</strong> structure). This structure contains information such as
310the file name, the document type, and a <strong>root</strong> pointer which
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]311is the root of the document (or more exactly the first child under the root
312which is the document). The tree is made of <strong>xmlNode</strong>s, chained
313in double linked lists of siblings and with childs&lt;->parent relationship.
314An xmlNode can also carry properties (a chain of xmlAttr structures). An
315attribute may have a value which is a list of TEXT or ENTITY_REF nodes.</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]316
317<p>Here is an example (erroneous w.r.t. the XML spec since there should be
318only one ELEMENT under the root):</p>
319
320<p><img src="structure.gif" alt=" structure.gif "></p>
321
322<p>In the source package there is a small program (not installed by default)
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]323called <strong>tester</strong> which parses XML files given as argument and
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]324prints them back as parsed. This is useful to detect errors both in XML code
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]325and in the XML parser itself. It has an option <strong>--debug</strong> which
326prints the actual in-memory structure of the document, here is the result with
327the <a href="#example">example</a> given before:</p>
328<pre>DOCUMENT
329version=1.0
330standalone=true
331 ELEMENT EXAMPLE
332 ATTRIBUTE prop1
333 TEXT
334 content=gnome is great
335 ATTRIBUTE prop2
336 ENTITY_REF
337 TEXT
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]338 content= linux too
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]339 ELEMENT head
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]340 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]341 TEXT
342 content=Welcome to Gnome
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]343 ELEMENT chapter
344 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]345 TEXT
346 content=The Linux adventure
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]347 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]348 TEXT
349 content=bla bla bla ...
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]350 ELEMENT image
351 ATTRIBUTE href
352 TEXT
353 content=linus.gif
354 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]355 TEXT
356 content=...</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]357
358<p>This should be useful to learn the internal representation model.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]359
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]360<h2><a name="interface">The SAX interface</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]361
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]362<p>Sometimes the DOM tree output is just too large to fit reasonably into
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]363memory. In that case and if you don't expect to save back the XML document
364loaded using libxml, it's better to use the SAX interface of libxml. SAX is a
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]365<strong>callback-based interface</strong> to the parser. Before parsing, the
366application layer registers a customized set of callbacks which are called
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]367by the library as it progresses through the XML input.</p>
368
369<p>To get a more detailed step-by-step guidance on using the SAX interface of
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]370libxml, <a href="mailto:james@daa.com.au">James Henstridge</a> has written <a
371href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">some nice
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]372documentation.</a></p>
373
374<p>You can debug the SAX behaviour by using the <strong>testSAX</strong>
375program located in the gnome-xml module (it's usually not shipped in the
376binary packages of libxml, but you can also find it in the tar source
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]377distribution). Here is the sequence of callbacks that would be reported by
378testSAX when parsing the example given before:</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]379<pre>SAX.setDocumentLocator()
380SAX.startDocument()
381SAX.getEntity(amp)
382SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp;amp; linux too')
383SAX.characters( , 3)
384SAX.startElement(head)
385SAX.characters( , 4)
386SAX.startElement(title)
387SAX.characters(Welcome to Gnome, 16)
388SAX.endElement(title)
389SAX.characters( , 3)
390SAX.endElement(head)
391SAX.characters( , 3)
392SAX.startElement(chapter)
393SAX.characters( , 4)
394SAX.startElement(title)
395SAX.characters(The Linux adventure, 19)
396SAX.endElement(title)
397SAX.characters( , 4)
398SAX.startElement(p)
399SAX.characters(bla bla bla ..., 15)
400SAX.endElement(p)
401SAX.characters( , 4)
402SAX.startElement(image, href='linus.gif')
403SAX.endElement(image)
404SAX.characters( , 4)
405SAX.startElement(p)
406SAX.characters(..., 3)
407SAX.endElement(p)
408SAX.characters( , 3)
409SAX.endElement(chapter)
410SAX.characters( , 1)
411SAX.endElement(EXAMPLE)
412SAX.endDocument()</pre>
413
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]414<p>Most of the other functionalities of libxml are based on the DOM
415tree-building facility, so nearly everything up to the end of this document
416presupposes the use of the standard DOM tree build. Note that the DOM tree
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]417itself is built by a set of registered default callbacks, without internal
418specific interface.</p>
419
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]420<h2><a name="library">The XML library interfaces</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]421
422<p>This section is directly intended to help programmers getting bootstrapped
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]423using the XML library from the C language. It doesn't intent to be extensive,
424I hope the automatically generated docs will provide the completeness
425required, but as a separated set of documents. The interfaces of the XML
426library are by principle low level, there is nearly zero abstration. Those
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]427interested in a higher level API should <a href="#DOM">look at DOM</a>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]428
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]429<p>The <a href="gnome-xml-parser.html">parser interfaces for XML</a> are
430separated from the <a href="gnome-xml-htmlparser.html">HTML parser ones</a>,
431let's have a look at how it can be called:</p>
432
433<h3><a name="Invoking">Invoking the parser : the pull way</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]434
435<p>Usually, the first thing to do is to read an XML input, the parser accepts
436to parse both memory mapped documents or direct files. The functions are
437defined in "parser.h":</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]438<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]439 <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
440 <dd><p>parse a zero terminated string containing the document</p>
441 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]442</dl>
443<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]444 <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
445 <dd><p>parse an XML document contained in a file (possibly compressed)</p>
446 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]447</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]448
449<p>This returns a pointer to the document structure (or NULL in case of
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]450failure).</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]451
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]452<h3 id="Invoking1">Invoking the parser: the push way</h3>
453
454<p>In order for the application to keep the control when the document is been
455fetched (common for GUI based programs) the libxml, as of version 1.8.3
456provides a push interface too, here are the interfaces:</p>
457<pre>xmlParserCtxtPtr xmlCreatePushParserCtxt(xmlSAXHandlerPtr sax,
458 void *user_data,
459 const char *chunk,
460 int size,
461 const char *filename);
462int xmlParseChunk (xmlParserCtxtPtr ctxt,
463 const char *chunk,
464 int size,
465 int terminate);</pre>
466
467<p>and here is a simple use example:</p>
468<pre> FILE *f;
469
470 f = fopen(filename, "r");
471 if (f != NULL) {
472 int res, size = 1024;
473 char chars[1024];
474 xmlParserCtxtPtr ctxt;
475
476 res = fread(chars, 1, 4, f);
477 if (res > 0) {
478 ctxt = xmlCreatePushParserCtxt(NULL, NULL,
479 chars, res, filename);
480 while ((res = fread(chars, 1, size, f)) > 0) {
481 xmlParseChunk(ctxt, chars, res, 0);
482 }
483 xmlParseChunk(ctxt, chars, 0, 1);
484 doc = ctxt->myDoc;
485 xmlFreeParserCtxt(ctxt);
486 }
487 }</pre>
488
489<p>Also note that the HTML parser embedded into libxml also have a push
490interface they are just prefixed by "html" instead of "xml"</p>
491
492<h3 id="Invoking2">Invoking the parser: the SAX interface</h3>
493
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]494<p>A couple of comments can be made, first this mean that the parser is
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]495memory-hungry, first to load the document in memory, second to build the tree.
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]496Reading a document without building the tree is possible using the SAX
497interfaces (see SAX.h and <a
498href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">James
499Henstridge documentation</a>), not also that the push interface can be limited
500to SAX, just use the two first arguments of
501<code>xmlCreatePushParserCtxt()</code>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]502
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]503<h3><a name="Building">Building a tree from scratch</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]504
505<p>The other way to get an XML tree in memory is by building it. Basically
506there is a set of functions dedicated to building new elements, those are also
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]507described in "tree.h", here is for example the piece of code producing the
508example used before:</p>
509<pre> xmlDocPtr doc;
510 xmlNodePtr tree, subtree;
511
512 doc = xmlNewDoc("1.0");
513 doc->root = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL);
514 xmlSetProp(doc->root, "prop1", "gnome is great");
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]515 xmlSetProp(doc->root, "prop2", "&amp; linux too");
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]516 tree = xmlNewChild(doc->root, NULL, "head", NULL);
517 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome");
518 tree = xmlNewChild(doc->root, NULL, "chapter", NULL);
519 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure");
520 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ...");
521 subtree = xmlNewChild(tree, NULL, "image", NULL);
522 xmlSetProp(subtree, "href", "linus.gif");</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]523
524<p>Not really rocket science ...</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]525
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]526<h3><a name="Traversing">Traversing the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]527
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]528<p>Basically by <a href="gnome-xml-tree.html">including "tree.h"</a> your code
529has access to the internal structure of all the element of the tree. The names
530should be somewhat simple like <strong>parent</strong>,
531<strong>childs</strong>, <strong>next</strong>, <strong>prev</strong>,
532<strong>properties</strong>, etc... For example still with the previous
533example:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]534<pre><code>doc->root->childs->childs</code></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]535
536<p>points to the title element,</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]537<pre>doc->root->childs->next->child->child</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]538
539<p>points to the text node containing the chapter titlle "The Linux adventure"
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]540and</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]541
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]542<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
543present before the document root, so doc->root may point to an element which
544is not the document Root Element, a function
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]545<code>xmlDocGetRootElement()</code> was added for this purpose.</p>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]546
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]547<h3><a name="Modifying">Modifying the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]548
Daniel Veillard0142b842000-01-14 14:45:24 +0000[diff] [blame]549<p>functions are provided to read and write the document content, here is an
550excerpt from the <a href="gnome-xml-tree.html">tree API</a>:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]551<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]552 <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
553 xmlChar *value);</code></dt>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]554 <dd><p>This set (or change) an attribute carried by an ELEMENT node the
555 value can be NULL</p>
556 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]557</dl>
558<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]559 <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]560 *name);</code></dt>
561 <dd><p>This function returns a pointer to the property content, note that
562 no extra copy is made</p>
563 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]564</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]565
566<p>Two functions must be used to read an write the text associated to
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]567elements:</p>
568<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]569 <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]570 *value);</code></dt>
571 <dd><p>This function takes an "external" string and convert it to one text
572 node or possibly to a list of entity and text nodes. All non-predefined
573 entity references like &amp;Gnome; will be stored internally as an
574 entity node, hence the result of the function may not be a single
575 node.</p>
576 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]577</dl>
578<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]579 <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]580 inLine);</code></dt>
581 <dd><p>this is the dual function, which generate a new string containing
582 the content of the text and entity nodes. Note the extra argument
583 inLine, if set to 1 instead of returning the &amp;Gnome; XML encoding in
584 the string it will substitute it with it's value say "GNU Network Object
585 Model Environment". Set it if you want to use the string for non XML
586 usage like User Interface.</p>
587 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]588</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]589
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]590<h3><a name="Saving">Saving a tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]591
592<p>Basically 3 options are possible:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]593<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]594 <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]595 *size);</code></dt>
596 <dd><p>returns a buffer where the document has been saved</p>
597 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]598</dl>
599<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]600 <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
601 <dd><p>dumps a buffer to an open file descriptor</p>
602 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]603</dl>
604<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]605 <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
606 <dd><p>save the document ot a file. In that case the compression interface
607 is triggered if turned on</p>
608 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]609</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]610
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]611<h3><a name="Compressio">Compression</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]612
613<p>The library handle transparently compression when doing file based
614accesses, the level of compression on saves can be tuned either globally or
615individually for one file:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]616<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]617 <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
618 <dd><p>Get the document compression ratio (0-9)</p>
619 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]620</dl>
621<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]622 <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
623 <dd><p>Set the document compression ratio</p>
624 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]625</dl>
626<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]627 <dt><code>int xmlGetCompressMode(void);</code></dt>
628 <dd><p>Get the default compression ratio</p>
629 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]630</dl>
631<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]632 <dt><code>void xmlSetCompressMode(int mode);</code></dt>
633 <dd><p>set the default compression ratio</p>
634 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]635</dl>
636
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]637<h2><a name="Entities">Entities or no entities</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]638
639<p>Entities principle is similar to simple C macros. They define an
640abbreviation for a given string that you can reuse many time through the
641content of your document. They are especially useful when frequent occurrences
642of a given string may occur within a document or to confine the change needed
643to a document to a restricted area in the internal subset of the document (at
644the beginning). Example:</p>
645<pre>1 &lt;?xml version="1.0"?>
6462 &lt;!DOCTYPE EXAMPLE SYSTEM "example.dtd" [
6473 &lt;!ENTITY xml "Extensible Markup Language">
6484 ]>
6495 &lt;EXAMPLE>
6506 &amp;xml;
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]6517 &lt;/EXAMPLE></pre>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]652
653<p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]654it's name with '&amp;' and following it by ';' without any spaces added. There
655are 5 predefined entities in libxml allowing to escape charaters with
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]656predefined meaning in some parts of the xml document content:
657<strong>&amp;lt;</strong> for the letter '&lt;', <strong>&amp;gt;</strong> for
658the letter '>', <strong>&amp;apos;</strong> for the letter ''',
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]659<strong>&amp;quot;</strong> for the letter '"', and <strong>&amp;amp;</strong>
660for the letter '&amp;'.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]661
662<p>One of the problems related to entities is that you may want the parser to
663substitute entities content to see the replacement text in your application,
664or you may prefer keeping entities references as such in the content to be
665able to save the document back without loosing this usually precious
666information (if the user went through the pain of explicitley defining
667entities, he may have a a rather negative attitude if you blindly susbtitute
668them as saving time). The function <a
669href="gnome-xml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a>
670allows to check and change the behaviour, which is to not substitute entities
671by default.</p>
672
673<p>Here is the DOM tree built by libxml for the previous document in the
674default case:</p>
675<pre>/gnome/src/gnome-xml -> ./tester --debug test/ent1
676DOCUMENT
677version=1.0
678 ELEMENT EXAMPLE
679 TEXT
680 content=
681 ENTITY_REF
682 INTERNAL_GENERAL_ENTITY xml
683 content=Extensible Markup Language
684 TEXT
685 content=</pre>
686
687<p>And here is the result when substituting entities:</p>
688<pre>/gnome/src/gnome-xml -> ./tester --debug --noent test/ent1
689DOCUMENT
690version=1.0
691 ELEMENT EXAMPLE
692 TEXT
693 content= Extensible Markup Language</pre>
694
695<p>So entities or no entities ? Basically it depends on your use case, I
696suggest to keep the non-substituting default behaviour and avoid using
697entities in your XML document or data if you are not willing to handle the
698entity references elements in the DOM tree.</p>
699
700<p>Note that at save time libxml enforce the conversion of the predefined
701entities where necessary to prevent well-formedness problems, and will also
702transparently replace those with chars (i.e. will not generate entity
703reference elements in the DOM tree nor call the reference() SAX callback when
704finding them in the input).</p>
705
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]706<h2><a name="Namespaces">Namespaces</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]707
708<p>The libxml library implement namespace @@ support by recognizing namespace
709contructs in the input, and does namespace lookup automatically when building
710the DOM tree. A namespace declaration is associated with an in-memory
711structure and all elements or attributes within that namespace point to it.
712Hence testing the namespace is a simple and fast equality operation at the
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]713user level.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]714
715<p>I suggest it that people using libxml use a namespace, and declare it on
716the root element of their document as the default namespace. Then they dont
717need to happend the prefix in the content but we will have a basis for future
718semantic refinement and merging of data from different sources. This doesn't
719augment significantly the size of the XML output, but significantly increase
720it's value in the long-term.</p>
721
722<p>Concerning the namespace value, this has to be an URL, but this doesn't
723have to point to any existing resource on the Web. I suggest using an URL
724within a domain you control, which makes sense and if possible holding some
725kind of versionning informations. For example
726<code>"http://www.gnome.org/gnumeric/1.0"</code> is a good namespace scheme.
727Then when you load a file, make sure that a namespace carrying the
728version-independant prefix is installed on the root element of your document,
729and if the version information don't match something you know, warn the user
730and be liberal in what you accept as the input. Also do *not* try to base
731namespace checking on the prefix value &lt;foo:text> may be exactly the same
732as &lt;bar:text> in another document, what really matter is the URI
733associated with the element or the attribute, not the prefix string which is
734just a shortcut for the full URI.</p>
735
736<p>@@Interfaces@@</p>
737
738<p>@@Examples@@</p>
739
740<p>Usually people object using namespace in the case of validation, I object
741this and will make sure that using namespaces won't break validity checking,
742so even is you plan or are using validation I strongly suggest to add
743namespaces to your document. A default namespace scheme
744<code>xmlns="http://...."</code> should not break validity even on less
745flexible parsers. Now using namespace to mix and differenciate content coming
746from mutliple Dtd will certainly break current validation schemes, I will try
747to provide ways to do this, but this may not be portable or standardized.</p>
748
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]749<h2><a name="Validation">Validation, or are you afraid of DTDs ?</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]750
751<p>Well what is validation and what is a DTD ?</p>
752
753<p>Validation is the process of checking a document against a set of
754construction rules, a <strong>DTD</strong> (Document Type Definition) is such
755a set of rules.</p>
756
757<p>The validation process and building DTDs are the two most difficult parts
758of XML life cycle. Briefly a DTD defines all the possibles element to be
759found within your document, what is the formal shape of your document tree (by
760defining the allowed content of an element, either text, a regular expression
761for the allowed list of children, or mixed content i.e. both text and childs).
762The DTD also defines the allowed attributes for all elements and the types of
763the attributes. For more detailed informations, I suggest to read the related
764parts of the XML specification, the examples found under
765gnome-xml/test/valid/dtd and the large amount of books available on XML. The
766dia example in gnome-xml/test/valid should be both simple and complete enough
767to allow you to build your own.</p>
768
769<p>A word of warning, building a good DTD which will fit your needs of your
770application in the long-term is far from trivial, however the extra level of
771quality it can insure is well worth the price for some sets of applications or
772if you already have already a DTD defined for your application field.</p>
773
774<p>The validation is not completely finished but in a (very IMHO) usable
775state. Until a real validation interface is defined the way to do it is to
776define and set the <strong>xmlDoValidityCheckingDefaultValue</strong> external
777variable to 1, this will of course be changed at some point:</p>
778
779<p>extern int xmlDoValidityCheckingDefaultValue;</p>
780
781<p>...</p>
782
783<p>xmlDoValidityCheckingDefaultValue = 1;</p>
784
785<p></p>
786
787<p>To handle external entities, use the function
788<strong>xmlSetExternalEntityLoader</strong>(xmlExternalEntityLoader f); to
789link in you HTTP/FTP/Entities database library to the standard libxml
790core.</p>
791
792<p>@@interfaces@@</p>
793
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]794<h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]795
796<p><a href="http://www.w3.org/DOM/">DOM</a> stands for the <em>Document Object
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]797Model</em> this is an API for accessing XML or HTML structured documents.
798Native support for DOM in Gnome is on the way (module gnome-dom), and it will
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]799be based on gnome-xml. This will be a far cleaner interface to manipulate XML
Daniel Veillardc08a2c61999-09-08 21:35:25 +0000[diff] [blame]800files within Gnome since it won't expose the internal structure. DOM defines a
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]801set of IDL (or Java) interfaces allowing to traverse and manipulate a
802document. The DOM library will allow accessing and modifying "live" documents
803presents on other programs like this:</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]804
805<p><img src="DOM.gif" alt=" DOM.gif "></p>
806
807<p>This should help greatly doing things like modifying a gnumeric spreadsheet
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]808embedded in a GWP document for example.</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]809
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]810<p>The current DOM implementation on top of libxml is the <a
811href="http://cvs.gnome.org/lxr/source/gdome/">gdome Gnome module</a>, this is
812a full DOM interface, thanks to <a href="mailto:raph@levien.com">Raph
813Levien</a>.</p>
814
815<p>The gnome-dom module in the Gnome CVS base is obsolete</p>
816
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]817<h2><a name="Example"></a><a name="real">A real example</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]818
819<p>Here is a real size example, where the actual content of the application
820data is not kept in the DOM tree but uses internal structures. It is based on
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]821a proposal to keep a database of jobs related to Gnome, with an XML based
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]822storage structure. Here is an <a href="gjobs.xml">XML encoded jobs
823base</a>:</p>
824<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]825&lt;gjob:Helping xmlns:gjob="http://www.gnome.org/some-location">
826 &lt;gjob:Jobs>
827
828 &lt;gjob:Job>
829 &lt;gjob:Project ID="3"/>
830 &lt;gjob:Application>GBackup&lt;/gjob:Application>
831 &lt;gjob:Category>Development&lt;/gjob:Category>
832
833 &lt;gjob:Update>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]834 &lt;gjob:Status>Open&lt;/gjob:Status>
835 &lt;gjob:Modified>Mon, 07 Jun 1999 20:27:45 -0400 MET DST&lt;/gjob:Modified>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]836 &lt;gjob:Salary>USD 0.00&lt;/gjob:Salary>
837 &lt;/gjob:Update>
838
839 &lt;gjob:Developers>
840 &lt;gjob:Developer>
841 &lt;/gjob:Developer>
842 &lt;/gjob:Developers>
843
844 &lt;gjob:Contact>
845 &lt;gjob:Person>Nathan Clemons&lt;/gjob:Person>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]846 &lt;gjob:Email>nathan@windsofstorm.net&lt;/gjob:Email>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]847 &lt;gjob:Company>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]848 &lt;/gjob:Company>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]849 &lt;gjob:Organisation>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]850 &lt;/gjob:Organisation>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]851 &lt;gjob:Webpage>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]852 &lt;/gjob:Webpage>
853 &lt;gjob:Snailmail>
854 &lt;/gjob:Snailmail>
855 &lt;gjob:Phone>
856 &lt;/gjob:Phone>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]857 &lt;/gjob:Contact>
858
859 &lt;gjob:Requirements>
860 The program should be released as free software, under the GPL.
861 &lt;/gjob:Requirements>
862
863 &lt;gjob:Skills>
864 &lt;/gjob:Skills>
865
866 &lt;gjob:Details>
867 A GNOME based system that will allow a superuser to configure
868 compressed and uncompressed files and/or file systems to be backed
869 up with a supported media in the system. This should be able to
870 perform via find commands generating a list of files that are passed
871 to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine
872 or via operations performed on the filesystem itself. Email
873 notification and GUI status display very important.
874 &lt;/gjob:Details>
875
876 &lt;/gjob:Job>
877
878 &lt;/gjob:Jobs>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]879&lt;/gjob:Helping></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]880
881<p>While loading the XML file into an internal DOM tree is a matter of calling
882only a couple of functions, browsing the tree to gather the informations and
883generate the internals structures is harder, and more error prone.</p>
884
885<p>The suggested principle is to be tolerant with respect to the input
886structure. For example the ordering of the attributes is not significant, Cthe
887XML specification is clear about it. It's also usually a good idea to not be
888dependant of the orders of the childs of a given node, unless it really makes
889things harder. Here is some code to parse the informations for a person:</p>
890<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]891 * A person record
892 */
893typedef struct person {
894 char *name;
895 char *email;
896 char *company;
897 char *organisation;
898 char *smail;
899 char *webPage;
900 char *phone;
901} person, *personPtr;
902
903/*
904 * And the code needed to parse it
905 */
906personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
907 personPtr ret = NULL;
908
909DEBUG("parsePerson\n");
910 /*
911 * allocate the struct
912 */
913 ret = (personPtr) malloc(sizeof(person));
914 if (ret == NULL) {
915 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]916 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]917 }
918 memset(ret, 0, sizeof(person));
919
920 /* We don't care what the top level element name is */
921 cur = cur->childs;
922 while (cur != NULL) {
923 if ((!strcmp(cur->name, "Person")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]924 ret->name = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]925 if ((!strcmp(cur->name, "Email")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]926 ret->email = xmlNodeListGetString(doc, cur->childs, 1);
927 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]928 }
929
930 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]931}</pre>
932
933<p>Here is a couple of things to notice:</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]934<ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]935 <li>Usually a recursive parsing style is the more convenient one, XML data
936 being by nature subject to repetitive constructs and usualy exibit highly
937 stuctured patterns.</li>
938 <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, i.e.
939 the pointer to the global XML document and the namespace reserved to the
940 application. Document wide information are needed for example to decode
941 entities and it's a good coding practice to define a namespace for your
942 application set of data and test that the element and attributes you're
943 analyzing actually pertains to your application space. This is done by a
944 simple equality test (cur->ns == ns).</li>
945 <li>To retrieve text and attributes value, it is suggested to use the
946 function <em>xmlNodeListGetString</em> to gather all the text and entity
947 reference nodes generated by the DOM output and produce an single text
948 string.</li>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]949</ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]950
951<p>Here is another piece of code used to parse another level of the
952structure:</p>
953<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]954 * a Description for a Job
955 */
956typedef struct job {
957 char *projectID;
958 char *application;
959 char *category;
960 personPtr contact;
961 int nbDevelopers;
962 personPtr developers[100]; /* using dynamic alloc is left as an exercise */
963} job, *jobPtr;
964
965/*
966 * And the code needed to parse it
967 */
968jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
969 jobPtr ret = NULL;
970
971DEBUG("parseJob\n");
972 /*
973 * allocate the struct
974 */
975 ret = (jobPtr) malloc(sizeof(job));
976 if (ret == NULL) {
977 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]978 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]979 }
980 memset(ret, 0, sizeof(job));
981
982 /* We don't care what the top level element name is */
983 cur = cur->childs;
984 while (cur != NULL) {
985
986 if ((!strcmp(cur->name, "Project")) &amp;&amp; (cur->ns == ns)) {
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]987 ret->projectID = xmlGetProp(cur, "ID");
988 if (ret->projectID == NULL) {
989 fprintf(stderr, "Project has no ID\n");
990 }
991 }
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]992 if ((!strcmp(cur->name, "Application")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]993 ret->application = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]994 if ((!strcmp(cur->name, "Category")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]995 ret->category = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]996 if ((!strcmp(cur->name, "Contact")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]997 ret->contact = parsePerson(doc, ns, cur);
998 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]999 }
1000
1001 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]1002}</pre>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]1003
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]1004<p>One can notice that once used to it, writing this kind of code is quite
1005simple, but boring. Ultimately, it could be possble to write stubbers taking
1006either C data structure definitions, a set of XML examples or an XML DTD and
1007produce the code needed to import and export the content between C data and
1008XML storage. This is left as an exercise to the reader :-)</p>
1009
1010<p>Feel free to use <a href="gjobread.c">the code for the full C parsing
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]1011example</a> as a template, it is also available with Makefile in the Gnome CVS
1012base under gnome-xml/example</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]1013
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]1014<p></p>
1015
1016<p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>
1017
Daniel Veillard402e8c82000-02-29 22:57:47 +0000[diff] [blame^]1018<p>$Id: xml.html,v 1.24 2000/01/30 20:00:06 veillard Exp $</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]1019</body>
1020</html>