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gerrit-public.fairphone.software / platform / external / libxml2 / f84f71f4739f8df98eaa2d1e014653b8c8e9c63a / . / doc / xml.html
blob: 0bc1cbcb02bbee7d9ee05c9be529182c534bbaa3 [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>
26 <li><a href="#Invoking">Invoking the parser</a></li>
27 <li><a href="#Building">Building a tree from scratch</a></li>
28 <li><a href="#Traversing">Traversing the tree</a></li>
29 <li><a href="#Modifying">Modifying the tree</a></li>
30 <li><a href="#Saving">Saving the tree</a></li>
31 <li><a href="#Compressio">Compression</a></li>
32 </ul>
33 </li>
34 <li><a href="#Entities">Entities or no entities</a></li>
35 <li><a href="#Namespaces">Namespaces</a></li>
36 <li><a href="#Validation">Validation</a></li>
37 <li><a href="#Principles">DOM principles</a></li>
38 <li><a href="#real">A real example</a></li>
39</ul>
40
41<h2><a name="Introducti">Introduction</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]42
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]43<p>This document describes the <a href="http://www.w3.org/XML/">XML</a>
44library provideed in the <a href="http://www.gnome.org/">Gnome</a> framework.
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]45XML is a standard to build tag based structured documents/data.</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]46
47<p>The internal document repesentation is as close as possible to the <a
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]48href="http://www.w3.org/DOM/">DOM</a> interfaces.</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]49
50<p>Libxml also has a <a href="http://www.megginson.com/SAX/index.html">SAX
51interface</a>, <a href="mailto:james@daa.com.au">James Henstridge</a> made <a
52href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">a nice
53documentation</a> expaining how to use it. The interface is as compatible as
54possible with <a href="http://www.jclark.com/xml/expat.html">Expat</a>
55one.</p>
56
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]57<p>There is also a mailing-list <a
Daniel Veillard6bd26dc1999-09-03 14:28:40 +0000[diff] [blame]58href="mailto:xml@rufus.w3.org">xml@rufus.w3.org</a> for libxml, with an <a
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]59href="http://xmlsoft.org/messages">on-line archive</a>. To subscribe to this
60majordomo based list, send a mail to <a
Daniel Veillard6bd26dc1999-09-03 14:28:40 +0000[diff] [blame]61href="mailto:majordomo@rufus.w3.org">majordomo@rufus.w3.org</a> with
62"subscribe xml" in the <strong>content</strong> of the message.</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]63
64<p>This library is released both under the W3C Copyright and the GNU LGP,
65basically everybody should be happy, if not, drop me a mail.</p>
66
67<p>People are invited to use the <a
68href="http://cvs.gnome.org/lxr/source/gdome/">gdome Gnome module to</a> get a
69full DOM interface, thanks to <a href="mailto:raph@levien.com">Raph
70Levien</a>, check his <a
71href="http://www.levien.com/gnome/domination.html">DOMination paper</a>. He
72uses it for his implementation of <a
73href="http://www.w3.org/Graphics/SVG/">SVG</a> called <a
74href="http://www.levien.com/svg/">gill</a>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]75
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]76<h2><a name="Documentat">Documentation</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]77
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]78<p>The code is commented in a <a href=""></a>way which allow <a
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]79href="http://xmlsoft.org/libxml.html">extensive documentation</a> to be
80automatically extracted.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]81
82<p>At some point I will change the back-end to produce XML documentation in
83addition to SGML Docbook and HTML.</p>
84
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]85<h3>Reporting bugs</h3>
86
87<p>Well bugs or missing features are always possible, and I will make a point
88of fixing them in a timely fashion. The best way it to <a
89href="http://bugs.gnome.org/db/pa/lgnome-xml.html">use the Gnome bug tracking
90database</a>. I look at reports there regulary and it's good to have a
91reminder when a bug is still open. Check the <a
92href="http://bugs.gnome.org/Reporting.html">instructions on reporting bugs</a>
93and be sure to specify thatthe bug is for the package gnome-xml.</p>
94
95<p>Alternately you can just send the bug to the <a
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]96href="mailto:xml@rufus.w3.org">xml@rufus.w3.org</a> list.</p>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]97
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]98<h2><a name="Downloads">Downloads</a></h2>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]99
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]100<p>Latest version is 1.8.1, you can find it on <a
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]101href="ftp://rpmfind.net/pub/veillard/">rpmfind.net</a> or on the <a
102href="ftp://ftp.gnome.org/pub/GNOME/MIRRORS.html">Gnome FTP server</a> either
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]103as a <a href="ftp://ftp.gnome.org/pub/GNOME/stable/sources/libxml/">source
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]104archive</a> or <a href="ftp://ftp.gnome.org/pub/GNOME/contrib/rpms/">RPMs
105packages</a>.</p>
106
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]107<p>Libxml is also available from 2 CVs bases:</p>
108<ul>
109 <li><p>The <a href="http://dev.w3.org/cvsweb/XML/">W3C CVS base</a>,
110 available read-only using the CVS pserver authentification:</p>
111 <pre>CVSROOT=:pserver:anonymous@dev.w3.org:/sources/public
112password: anonymous
113module: XML</pre>
114 </li>
115 <li><p>The <a
116 href="http://cvs.gnome.org/bonsai/rview.cgi?cvsroot=/cvs/gnome&amp;dir=gnome-xml">Gnome
117 CVS base</a>, Check the <a
118 href="http://developer.gnome.org/tools/cvs.html">Gnome CVS Tools</a> page,
119 the CVS module is <b>gnome-xml</b></p>
120 </li>
121</ul>
122
123<h2><a name="News">News</a></h2>
124
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]125<h3>CVS only : check the <a
126href="http://cvs.gnome.org/lxr/source/gnome-xml/ChangeLog">Changelog</a> file
127for really accurate description</h3>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]128<ul>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]129 <li>working on HTML and XML links recognition layers, get in touch with me
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]130 if you want to test those.</li>
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame^]131</ul>
132
133<h3>1.8.3: Jan 5 2000</h3>
134<ul>
135 <li>a Push interface for the XML and HTML parsers</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]136 <li>an shell like interface to the document tree (try tester --shell
137 :-)</li>
Daniel Veillarddbfd6411999-12-28 16:35:14 +0000[diff] [blame]138 <li>lots of bug fixes and improvement added over XMas hollidays</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]139 <li>fixed the DTD parsing code to work with the xhtml DTD</li>
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame^]140 <li>added xmlRemoveProp(), xmlRemoveID() and xmlRemoveRef()</li>
141 <li>Fixed bugs in xmlNewNs()</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]142 <li>External entity loading code has been revamped, now it uses
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame^]143 xmlLoadExternalEntity(), some fix on entities processing were added</li>
Daniel Veillard437b87b2000-01-03 17:30:46 +0000[diff] [blame]144 <li>cleaned up WIN32 includes of socket stuff</li>
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]145</ul>
146
147<h3>1.8.2: Dec 21 1999</h3>
148<ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]149 <li>I got another problem with includes and C++, I hope this issue is fixed
150 for good this time</li>
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]151 <li>Added a few tree modification functions: xmlReplaceNode,
152 xmlAddPrevSibling, xmlAddNextSibling, xmlNodeSetName and
153 xmlDocSetRootElement</li>
154 <li>Tried to improve the HTML output with help from <a
155 href="mailto:clahey@umich.edu">Chris Lahey</a></li>
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]156</ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]157
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]158<h3>1.8.1: Dec 18 1999</h3>
159<ul>
160 <li>various patches to avoid troubles when using libxml with C++ compilers
161 the "namespace" keyword and C escaping in include files</li>
162 <li>a problem in one of the core macros IS_CHAR was corrected</li>
163 <li>fixed a bug introduced in 1.8.0 breaking default namespace processing,
164 and more specifically the Dia application</li>
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]165 <li>fixed a posteriori validation (validation after parsing, or by using a
166 Dtd not specified in the original document)</li>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]167 <li>fixed a bug in</li>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]168</ul>
169
170<h3>1.8.0: Dec 12 1999</h3>
171<ul>
172 <li>cleanup, especially memory wise</li>
173 <li>the parser should be more reliable, especially the HTML one, it should
174 not crash, whatever the input !</li>
175 <li>Integrated various patches, especially a speedup improvement for large
176 dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>,
177 configure with --with-buffers to enable them.</li>
178 <li>attribute normalization, oops should have been added long ago !</li>
179 <li>attributes defaulted from Dtds should be available, xmlSetProp() now
180 does entities escapting by default.</li>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]181</ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]182
183<h3>1.7.4: Oct 25 1999</h3>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]184<ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]185 <li>Lots of HTML improvement</li>
186 <li>Fixed some errors when saving both XML and HTML</li>
187 <li>More examples, the regression tests should now look clean</li>
188 <li>Fixed a bug with contiguous charref</li>
189</ul>
190
191<h3>1.7.3: Sep 29 1999</h3>
192<ul>
193 <li>portability problems fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]194 <li>snprintf was used unconditionnally, leading to link problems on system
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]195 were it's not available, fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]196</ul>
197
198<h3>1.7.1: Sep 24 1999</h3>
199<ul>
200 <li>The basic type for strings manipulated by libxml has been renamed in
201 1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason
202 is that CHAR was conflicting with a predefined type on Windows. However on
203 non WIN32 environment, compatibility is provided by the way of a
204 <strong>#define </strong>.</li>
205 <li>Changed another error : the use of a structure field called errno, and
206 leading to troubles on platforms where it's a macro</li>
207</ul>
208
209<h3>1.7.0: sep 23 1999</h3>
210<ul>
211 <li>Added the ability to fetch remote DTD or parsed entities, see the <a
212 href="gnome-xml-nanohttp.html">nanohttp</a> module.</li>
213 <li>Added an errno to report errors by another mean than a simple printf
214 like callback</li>
215 <li>Finished ID/IDREF support and checking when validation</li>
216 <li>Serious memory leaks fixed (there is now a <a
217 href="gnome-xml-xmlmemory.html">memory wrapper</a> module)</li>
218 <li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a>
219 implementation</li>
220 <li>Added an HTML parser front-end</li>
221</ul>
222
223<h2><a name="XML">XML</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]224
225<p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for markup
226based structured documents, here is <a name="example">an example</a>:</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]227<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]228&lt;EXAMPLE prop1="gnome is great" prop2="&amp;amp; linux too">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]229 &lt;head>
230 &lt;title>Welcome to Gnome&lt;/title>
231 &lt;/head>
232 &lt;chapter>
233 &lt;title>The Linux adventure&lt;/title>
234 &lt;p>bla bla bla ...&lt;/p>
235 &lt;image href="linus.gif"/>
236 &lt;p>...&lt;/p>
237 &lt;/chapter>
238&lt;/EXAMPLE></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]239
240<p>The first line specify that it's an XML document and gives useful
241informations about it's encoding. Then the document is a text format whose
242structure is specified by tags between brackets. <strong>Each tag opened have
243to be closed</strong> XML is pedantic about this, not that for example the
244image tag has no content (just an attribute) and is closed by ending up the
245tag with <code>/></code>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]246
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]247<p>XML can be applied sucessfully to a wide range or usage from long term
248structured document maintenance where it follows the steps of SGML to simple
249data encoding mechanism like configuration file format (glade), spreadsheets
250(gnumeric), or even shorter lived document like in WebDAV where it is used to
251encode remote call between a client and a server.</p>
252
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]253<h2><a name="tree">The tree output</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]254
255<p>The parser returns a tree built during the document analysis. The value
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]256returned is an <strong>xmlDocPtr</strong> (i.e. a pointer to an
257<strong>xmlDoc</strong> structure). This structure contains informations like
258the file name, the document type, and a <strong>root</strong> pointer which
259is the root of the document (or more exactly the first child under the root
260which is the document). The tree is made of <strong>xmlNode</strong>s, chained
261in double linked lists of siblings and with childs&lt;->parent relationship.
262An xmlNode can also carry properties (a chain of xmlAttr structures). An
263attribute 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]264
265<p>Here is an example (erroneous w.r.t. the XML spec since there should be
266only one ELEMENT under the root):</p>
267
268<p><img src="structure.gif" alt=" structure.gif "></p>
269
270<p>In the source package there is a small program (not installed by default)
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]271called <strong>tester</strong> which parses XML files given as argument and
272prints them back as parsed, this is useful to detect errors both in XML code
273and in the XML parser itself. It has an option <strong>--debug</strong> which
274prints the actual in-memory structure of the document, here is the result with
275the <a href="#example">example</a> given before:</p>
276<pre>DOCUMENT
277version=1.0
278standalone=true
279 ELEMENT EXAMPLE
280 ATTRIBUTE prop1
281 TEXT
282 content=gnome is great
283 ATTRIBUTE prop2
284 ENTITY_REF
285 TEXT
286 content= too
287 ELEMENT head
288 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]289 TEXT
290 content=Welcome to Gnome
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]291 ELEMENT chapter
292 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]293 TEXT
294 content=The Linux adventure
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]295 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]296 TEXT
297 content=bla bla bla ...
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]298 ELEMENT image
299 ATTRIBUTE href
300 TEXT
301 content=linus.gif
302 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]303 TEXT
304 content=...</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]305
306<p>This should be useful to learn the internal representation model.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]307
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]308<h2><a name="interface">The SAX interface</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]309
310<p>Sometimes the DOM tree output is just to large to fit reasonably into
311memory. In that case and if you don't expect to save back the XML document
312loaded using libxml, it's better to use the SAX interface of libxml. SAX is a
313<strong>callback based interface</strong> to the parser. Before parsing, the
314application layer register a customized set of callbacks which will be called
315by the library as it progresses through the XML input.</p>
316
317<p>To get a more detailed step-by-step guidance on using the SAX interface of
318libxml, <a href="mailto:james@daa.com.au">James Henstridge</a> made <a
319href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">a nice
320documentation.</a></p>
321
322<p>You can debug the SAX behaviour by using the <strong>testSAX</strong>
323program located in the gnome-xml module (it's usually not shipped in the
324binary packages of libxml, but you can also find it in the tar source
325distribution). Here is the sequence of callback that would be generated when
326parsing the example given before as reported by testSAX:</p>
327<pre>SAX.setDocumentLocator()
328SAX.startDocument()
329SAX.getEntity(amp)
330SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp;amp; linux too')
331SAX.characters( , 3)
332SAX.startElement(head)
333SAX.characters( , 4)
334SAX.startElement(title)
335SAX.characters(Welcome to Gnome, 16)
336SAX.endElement(title)
337SAX.characters( , 3)
338SAX.endElement(head)
339SAX.characters( , 3)
340SAX.startElement(chapter)
341SAX.characters( , 4)
342SAX.startElement(title)
343SAX.characters(The Linux adventure, 19)
344SAX.endElement(title)
345SAX.characters( , 4)
346SAX.startElement(p)
347SAX.characters(bla bla bla ..., 15)
348SAX.endElement(p)
349SAX.characters( , 4)
350SAX.startElement(image, href='linus.gif')
351SAX.endElement(image)
352SAX.characters( , 4)
353SAX.startElement(p)
354SAX.characters(..., 3)
355SAX.endElement(p)
356SAX.characters( , 3)
357SAX.endElement(chapter)
358SAX.characters( , 1)
359SAX.endElement(EXAMPLE)
360SAX.endDocument()</pre>
361
362<p>Most of the other functionnalities of libxml are based on the DOM tree
363building facility, so nearly everything up to the end of this document
364presuppose the use of the standard DOM tree build. Note that the DOM tree
365itself is built by a set of registered default callbacks, without internal
366specific interface.</p>
367
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]368<h2><a name="library">The XML library interfaces</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]369
370<p>This section is directly intended to help programmers getting bootstrapped
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]371using the XML library from the C language. It doesn't intent to be extensive,
372I hope the automatically generated docs will provide the completeness
373required, but as a separated set of documents. The interfaces of the XML
374library are by principle low level, there is nearly zero abstration. Those
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]375interested in a higher level API should <a href="#DOM">look at DOM</a>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]376
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]377<h3><a name="Invoking">Invoking the parser</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]378
379<p>Usually, the first thing to do is to read an XML input, the parser accepts
380to parse both memory mapped documents or direct files. The functions are
381defined in "parser.h":</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]382<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]383 <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
384 <dd><p>parse a zero terminated string containing the document</p>
385 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]386</dl>
387<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]388 <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
389 <dd><p>parse an XML document contained in a file (possibly compressed)</p>
390 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]391</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]392
393<p>This returns a pointer to the document structure (or NULL in case of
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]394failure).</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]395
396<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]397memory-hungry, first to load the document in memory, second to build the tree.
398Reading a document without building the tree will be possible in the future by
399pluggin the code to the SAX interface (see SAX.c).</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]400
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]401<h3><a name="Building">Building a tree from scratch</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]402
403<p>The other way to get an XML tree in memory is by building it. Basically
404there is a set of functions dedicated to building new elements, those are also
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]405described in "tree.h", here is for example the piece of code producing the
406example used before:</p>
407<pre> xmlDocPtr doc;
408 xmlNodePtr tree, subtree;
409
410 doc = xmlNewDoc("1.0");
411 doc->root = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL);
412 xmlSetProp(doc->root, "prop1", "gnome is great");
413 xmlSetProp(doc->root, "prop2", "&amp;linux; too");
414 tree = xmlNewChild(doc->root, NULL, "head", NULL);
415 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome");
416 tree = xmlNewChild(doc->root, NULL, "chapter", NULL);
417 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure");
418 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ...");
419 subtree = xmlNewChild(tree, NULL, "image", NULL);
420 xmlSetProp(subtree, "href", "linus.gif");</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]421
422<p>Not really rocket science ...</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]423
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]424<h3><a name="Traversing">Traversing the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]425
426<p>Basically by including "tree.h" your code has access to the internal
427structure of all the element of the tree. The names should be somewhat simple
428like <strong>parent</strong>, <strong>childs</strong>, <strong>next</strong>,
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]429<strong>prev</strong>, <strong>properties</strong>, etc... For example still
430with the previous example:</p>
431<pre><code>doc->root->childs->childs</code></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]432
433<p>points to the title element,</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]434<pre>doc->root->childs->next->child->child</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]435
436<p>points to the text node containing the chapter titlle "The Linux adventure"
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]437and</p>
438<pre>doc->root->properties->next->val</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]439
440<p>points to the entity reference containing the value of "&amp;linux" at the
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]441beginning of the second attribute of the root element "EXAMPLE".</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]442
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]443<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
444present before the document root, so doc->root may point to an element which
445is not the document Root Element, a function
Daniel Veillard5cb5ab81999-12-21 15:35:29 +0000[diff] [blame]446<code>xmlDocGetRootElement()</code> was added for this purpose.</p>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]447
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]448<h3><a name="Modifying">Modifying the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]449
450<p>functions are provided to read and write the document content:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]451<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]452 <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
453 xmlChar *value);</code></dt>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]454 <dd><p>This set (or change) an attribute carried by an ELEMENT node the
455 value can be NULL</p>
456 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]457</dl>
458<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]459 <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]460 *name);</code></dt>
461 <dd><p>This function returns a pointer to the property content, note that
462 no extra copy is made</p>
463 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]464</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]465
466<p>Two functions must be used to read an write the text associated to
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]467elements:</p>
468<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]469 <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]470 *value);</code></dt>
471 <dd><p>This function takes an "external" string and convert it to one text
472 node or possibly to a list of entity and text nodes. All non-predefined
473 entity references like &amp;Gnome; will be stored internally as an
474 entity node, hence the result of the function may not be a single
475 node.</p>
476 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]477</dl>
478<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]479 <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]480 inLine);</code></dt>
481 <dd><p>this is the dual function, which generate a new string containing
482 the content of the text and entity nodes. Note the extra argument
483 inLine, if set to 1 instead of returning the &amp;Gnome; XML encoding in
484 the string it will substitute it with it's value say "GNU Network Object
485 Model Environment". Set it if you want to use the string for non XML
486 usage like User Interface.</p>
487 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]488</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]489
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]490<h3><a name="Saving">Saving a tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]491
492<p>Basically 3 options are possible:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]493<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]494 <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]495 *size);</code></dt>
496 <dd><p>returns a buffer where the document has been saved</p>
497 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]498</dl>
499<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]500 <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
501 <dd><p>dumps a buffer to an open file descriptor</p>
502 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]503</dl>
504<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]505 <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
506 <dd><p>save the document ot a file. In that case the compression interface
507 is triggered if turned on</p>
508 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]509</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]510
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]511<h3><a name="Compressio">Compression</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]512
513<p>The library handle transparently compression when doing file based
514accesses, the level of compression on saves can be tuned either globally or
515individually for one file:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]516<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]517 <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
518 <dd><p>Get the document compression ratio (0-9)</p>
519 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]520</dl>
521<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]522 <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
523 <dd><p>Set the document compression ratio</p>
524 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]525</dl>
526<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]527 <dt><code>int xmlGetCompressMode(void);</code></dt>
528 <dd><p>Get the default compression ratio</p>
529 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]530</dl>
531<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]532 <dt><code>void xmlSetCompressMode(int mode);</code></dt>
533 <dd><p>set the default compression ratio</p>
534 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]535</dl>
536
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]537<h2><a name="Entities">Entities or no entities</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]538
539<p>Entities principle is similar to simple C macros. They define an
540abbreviation for a given string that you can reuse many time through the
541content of your document. They are especially useful when frequent occurrences
542of a given string may occur within a document or to confine the change needed
543to a document to a restricted area in the internal subset of the document (at
544the beginning). Example:</p>
545<pre>1 &lt;?xml version="1.0"?>
5462 &lt;!DOCTYPE EXAMPLE SYSTEM "example.dtd" [
5473 &lt;!ENTITY xml "Extensible Markup Language">
5484 ]>
5495 &lt;EXAMPLE>
5506 &amp;xml;
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]5517 &lt;/EXAMPLE></pre>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]552
553<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]554it's name with '&amp;' and following it by ';' without any spaces added. There
555are 5 predefined entities in libxml allowing to escape charaters with
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]556predefined meaning in some parts of the xml document content:
557<strong>&amp;lt;</strong> for the letter '&lt;', <strong>&amp;gt;</strong> for
558the letter '>', <strong>&amp;apos;</strong> for the letter ''',
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]559<strong>&amp;quot;</strong> for the letter '"', and <strong>&amp;amp;</strong>
560for the letter '&amp;'.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]561
562<p>One of the problems related to entities is that you may want the parser to
563substitute entities content to see the replacement text in your application,
564or you may prefer keeping entities references as such in the content to be
565able to save the document back without loosing this usually precious
566information (if the user went through the pain of explicitley defining
567entities, he may have a a rather negative attitude if you blindly susbtitute
568them as saving time). The function <a
569href="gnome-xml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a>
570allows to check and change the behaviour, which is to not substitute entities
571by default.</p>
572
573<p>Here is the DOM tree built by libxml for the previous document in the
574default case:</p>
575<pre>/gnome/src/gnome-xml -> ./tester --debug test/ent1
576DOCUMENT
577version=1.0
578 ELEMENT EXAMPLE
579 TEXT
580 content=
581 ENTITY_REF
582 INTERNAL_GENERAL_ENTITY xml
583 content=Extensible Markup Language
584 TEXT
585 content=</pre>
586
587<p>And here is the result when substituting entities:</p>
588<pre>/gnome/src/gnome-xml -> ./tester --debug --noent test/ent1
589DOCUMENT
590version=1.0
591 ELEMENT EXAMPLE
592 TEXT
593 content= Extensible Markup Language</pre>
594
595<p>So entities or no entities ? Basically it depends on your use case, I
596suggest to keep the non-substituting default behaviour and avoid using
597entities in your XML document or data if you are not willing to handle the
598entity references elements in the DOM tree.</p>
599
600<p>Note that at save time libxml enforce the conversion of the predefined
601entities where necessary to prevent well-formedness problems, and will also
602transparently replace those with chars (i.e. will not generate entity
603reference elements in the DOM tree nor call the reference() SAX callback when
604finding them in the input).</p>
605
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]606<h2><a name="Namespaces">Namespaces</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]607
608<p>The libxml library implement namespace @@ support by recognizing namespace
609contructs in the input, and does namespace lookup automatically when building
610the DOM tree. A namespace declaration is associated with an in-memory
611structure and all elements or attributes within that namespace point to it.
612Hence testing the namespace is a simple and fast equality operation at the
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]613user level.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]614
615<p>I suggest it that people using libxml use a namespace, and declare it on
616the root element of their document as the default namespace. Then they dont
617need to happend the prefix in the content but we will have a basis for future
618semantic refinement and merging of data from different sources. This doesn't
619augment significantly the size of the XML output, but significantly increase
620it's value in the long-term.</p>
621
622<p>Concerning the namespace value, this has to be an URL, but this doesn't
623have to point to any existing resource on the Web. I suggest using an URL
624within a domain you control, which makes sense and if possible holding some
625kind of versionning informations. For example
626<code>"http://www.gnome.org/gnumeric/1.0"</code> is a good namespace scheme.
627Then when you load a file, make sure that a namespace carrying the
628version-independant prefix is installed on the root element of your document,
629and if the version information don't match something you know, warn the user
630and be liberal in what you accept as the input. Also do *not* try to base
631namespace checking on the prefix value &lt;foo:text> may be exactly the same
632as &lt;bar:text> in another document, what really matter is the URI
633associated with the element or the attribute, not the prefix string which is
634just a shortcut for the full URI.</p>
635
636<p>@@Interfaces@@</p>
637
638<p>@@Examples@@</p>
639
640<p>Usually people object using namespace in the case of validation, I object
641this and will make sure that using namespaces won't break validity checking,
642so even is you plan or are using validation I strongly suggest to add
643namespaces to your document. A default namespace scheme
644<code>xmlns="http://...."</code> should not break validity even on less
645flexible parsers. Now using namespace to mix and differenciate content coming
646from mutliple Dtd will certainly break current validation schemes, I will try
647to provide ways to do this, but this may not be portable or standardized.</p>
648
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]649<h2><a name="Validation">Validation, or are you afraid of DTDs ?</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]650
651<p>Well what is validation and what is a DTD ?</p>
652
653<p>Validation is the process of checking a document against a set of
654construction rules, a <strong>DTD</strong> (Document Type Definition) is such
655a set of rules.</p>
656
657<p>The validation process and building DTDs are the two most difficult parts
658of XML life cycle. Briefly a DTD defines all the possibles element to be
659found within your document, what is the formal shape of your document tree (by
660defining the allowed content of an element, either text, a regular expression
661for the allowed list of children, or mixed content i.e. both text and childs).
662The DTD also defines the allowed attributes for all elements and the types of
663the attributes. For more detailed informations, I suggest to read the related
664parts of the XML specification, the examples found under
665gnome-xml/test/valid/dtd and the large amount of books available on XML. The
666dia example in gnome-xml/test/valid should be both simple and complete enough
667to allow you to build your own.</p>
668
669<p>A word of warning, building a good DTD which will fit your needs of your
670application in the long-term is far from trivial, however the extra level of
671quality it can insure is well worth the price for some sets of applications or
672if you already have already a DTD defined for your application field.</p>
673
674<p>The validation is not completely finished but in a (very IMHO) usable
675state. Until a real validation interface is defined the way to do it is to
676define and set the <strong>xmlDoValidityCheckingDefaultValue</strong> external
677variable to 1, this will of course be changed at some point:</p>
678
679<p>extern int xmlDoValidityCheckingDefaultValue;</p>
680
681<p>...</p>
682
683<p>xmlDoValidityCheckingDefaultValue = 1;</p>
684
685<p></p>
686
687<p>To handle external entities, use the function
688<strong>xmlSetExternalEntityLoader</strong>(xmlExternalEntityLoader f); to
689link in you HTTP/FTP/Entities database library to the standard libxml
690core.</p>
691
692<p>@@interfaces@@</p>
693
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]694<h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]695
696<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]697Model</em> this is an API for accessing XML or HTML structured documents.
698Native 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]699be based on gnome-xml. This will be a far cleaner interface to manipulate XML
Daniel Veillardc08a2c61999-09-08 21:35:25 +0000[diff] [blame]700files within Gnome since it won't expose the internal structure. DOM defines a
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]701set of IDL (or Java) interfaces allowing to traverse and manipulate a
702document. The DOM library will allow accessing and modifying "live" documents
703presents on other programs like this:</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]704
705<p><img src="DOM.gif" alt=" DOM.gif "></p>
706
707<p>This should help greatly doing things like modifying a gnumeric spreadsheet
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]708embedded in a GWP document for example.</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]709
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]710<p>The current DOM implementation on top of libxml is the <a
711href="http://cvs.gnome.org/lxr/source/gdome/">gdome Gnome module</a>, this is
712a full DOM interface, thanks to <a href="mailto:raph@levien.com">Raph
713Levien</a>.</p>
714
715<p>The gnome-dom module in the Gnome CVS base is obsolete</p>
716
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]717<h2><a name="Example"></a><a name="real">A real example</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]718
719<p>Here is a real size example, where the actual content of the application
720data 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]721a proposal to keep a database of jobs related to Gnome, with an XML based
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]722storage structure. Here is an <a href="gjobs.xml">XML encoded jobs
723base</a>:</p>
724<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]725&lt;gjob:Helping xmlns:gjob="http://www.gnome.org/some-location">
726 &lt;gjob:Jobs>
727
728 &lt;gjob:Job>
729 &lt;gjob:Project ID="3"/>
730 &lt;gjob:Application>GBackup&lt;/gjob:Application>
731 &lt;gjob:Category>Development&lt;/gjob:Category>
732
733 &lt;gjob:Update>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]734 &lt;gjob:Status>Open&lt;/gjob:Status>
735 &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]736 &lt;gjob:Salary>USD 0.00&lt;/gjob:Salary>
737 &lt;/gjob:Update>
738
739 &lt;gjob:Developers>
740 &lt;gjob:Developer>
741 &lt;/gjob:Developer>
742 &lt;/gjob:Developers>
743
744 &lt;gjob:Contact>
745 &lt;gjob:Person>Nathan Clemons&lt;/gjob:Person>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]746 &lt;gjob:Email>nathan@windsofstorm.net&lt;/gjob:Email>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]747 &lt;gjob:Company>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]748 &lt;/gjob:Company>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]749 &lt;gjob:Organisation>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]750 &lt;/gjob:Organisation>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]751 &lt;gjob:Webpage>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]752 &lt;/gjob:Webpage>
753 &lt;gjob:Snailmail>
754 &lt;/gjob:Snailmail>
755 &lt;gjob:Phone>
756 &lt;/gjob:Phone>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]757 &lt;/gjob:Contact>
758
759 &lt;gjob:Requirements>
760 The program should be released as free software, under the GPL.
761 &lt;/gjob:Requirements>
762
763 &lt;gjob:Skills>
764 &lt;/gjob:Skills>
765
766 &lt;gjob:Details>
767 A GNOME based system that will allow a superuser to configure
768 compressed and uncompressed files and/or file systems to be backed
769 up with a supported media in the system. This should be able to
770 perform via find commands generating a list of files that are passed
771 to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine
772 or via operations performed on the filesystem itself. Email
773 notification and GUI status display very important.
774 &lt;/gjob:Details>
775
776 &lt;/gjob:Job>
777
778 &lt;/gjob:Jobs>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]779&lt;/gjob:Helping></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]780
781<p>While loading the XML file into an internal DOM tree is a matter of calling
782only a couple of functions, browsing the tree to gather the informations and
783generate the internals structures is harder, and more error prone.</p>
784
785<p>The suggested principle is to be tolerant with respect to the input
786structure. For example the ordering of the attributes is not significant, Cthe
787XML specification is clear about it. It's also usually a good idea to not be
788dependant of the orders of the childs of a given node, unless it really makes
789things harder. Here is some code to parse the informations for a person:</p>
790<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]791 * A person record
792 */
793typedef struct person {
794 char *name;
795 char *email;
796 char *company;
797 char *organisation;
798 char *smail;
799 char *webPage;
800 char *phone;
801} person, *personPtr;
802
803/*
804 * And the code needed to parse it
805 */
806personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
807 personPtr ret = NULL;
808
809DEBUG("parsePerson\n");
810 /*
811 * allocate the struct
812 */
813 ret = (personPtr) malloc(sizeof(person));
814 if (ret == NULL) {
815 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]816 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]817 }
818 memset(ret, 0, sizeof(person));
819
820 /* We don't care what the top level element name is */
821 cur = cur->childs;
822 while (cur != NULL) {
823 if ((!strcmp(cur->name, "Person")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]824 ret->name = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]825 if ((!strcmp(cur->name, "Email")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]826 ret->email = xmlNodeListGetString(doc, cur->childs, 1);
827 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]828 }
829
830 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]831}</pre>
832
833<p>Here is a couple of things to notice:</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]834<ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]835 <li>Usually a recursive parsing style is the more convenient one, XML data
836 being by nature subject to repetitive constructs and usualy exibit highly
837 stuctured patterns.</li>
838 <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, i.e.
839 the pointer to the global XML document and the namespace reserved to the
840 application. Document wide information are needed for example to decode
841 entities and it's a good coding practice to define a namespace for your
842 application set of data and test that the element and attributes you're
843 analyzing actually pertains to your application space. This is done by a
844 simple equality test (cur->ns == ns).</li>
845 <li>To retrieve text and attributes value, it is suggested to use the
846 function <em>xmlNodeListGetString</em> to gather all the text and entity
847 reference nodes generated by the DOM output and produce an single text
848 string.</li>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]849</ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]850
851<p>Here is another piece of code used to parse another level of the
852structure:</p>
853<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]854 * a Description for a Job
855 */
856typedef struct job {
857 char *projectID;
858 char *application;
859 char *category;
860 personPtr contact;
861 int nbDevelopers;
862 personPtr developers[100]; /* using dynamic alloc is left as an exercise */
863} job, *jobPtr;
864
865/*
866 * And the code needed to parse it
867 */
868jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
869 jobPtr ret = NULL;
870
871DEBUG("parseJob\n");
872 /*
873 * allocate the struct
874 */
875 ret = (jobPtr) malloc(sizeof(job));
876 if (ret == NULL) {
877 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]878 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]879 }
880 memset(ret, 0, sizeof(job));
881
882 /* We don't care what the top level element name is */
883 cur = cur->childs;
884 while (cur != NULL) {
885
886 if ((!strcmp(cur->name, "Project")) &amp;&amp; (cur->ns == ns)) {
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]887 ret->projectID = xmlGetProp(cur, "ID");
888 if (ret->projectID == NULL) {
889 fprintf(stderr, "Project has no ID\n");
890 }
891 }
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]892 if ((!strcmp(cur->name, "Application")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]893 ret->application = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]894 if ((!strcmp(cur->name, "Category")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]895 ret->category = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]896 if ((!strcmp(cur->name, "Contact")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]897 ret->contact = parsePerson(doc, ns, cur);
898 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]899 }
900
901 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]902}</pre>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]903
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]904<p>One can notice that once used to it, writing this kind of code is quite
905simple, but boring. Ultimately, it could be possble to write stubbers taking
906either C data structure definitions, a set of XML examples or an XML DTD and
907produce the code needed to import and export the content between C data and
908XML storage. This is left as an exercise to the reader :-)</p>
909
910<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]911example</a> as a template, it is also available with Makefile in the Gnome CVS
912base under gnome-xml/example</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]913
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]914<p></p>
915
916<p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>
917
Daniel Veillardf84f71f2000-01-05 19:54:23 +0000[diff] [blame^]918<p>$Id: xml.html,v 1.19 2000/01/03 17:30:45 veillard Exp $</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]919</body>
920</html>