Gitiles
Code Review Sign In
gerrit-public.fairphone.software / platform / external / libxml2 / f600e2537f838e9806e80572e8e62abc5ff05d98 / . / doc / xml.html
blob: 819585e164f9f4f3a6a2ac946916eda6cd8a0356 [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 Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]131 <li>I got another problem with includes and C++, I hope this issue is fixed
132 for good this time</li>
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]133</ul>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]134
Daniel Veillarde4e51311999-12-18 15:32:46 +0000[diff] [blame]135<h3>1.8.1: Dec 18 1999</h3>
136<ul>
137 <li>various patches to avoid troubles when using libxml with C++ compilers
138 the "namespace" keyword and C escaping in include files</li>
139 <li>a problem in one of the core macros IS_CHAR was corrected</li>
140 <li>fixed a bug introduced in 1.8.0 breaking default namespace processing,
141 and more specifically the Dia application</li>
Daniel Veillard944b5ff1999-12-15 19:08:24 +0000[diff] [blame]142 <li>fixed a posteriori validation (validation after parsing, or by using a
143 Dtd not specified in the original document)</li>
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]144 <li>fixed a bug in</li>
Daniel Veillard10a2c651999-12-12 13:03:50 +0000[diff] [blame]145</ul>
146
147<h3>1.8.0: Dec 12 1999</h3>
148<ul>
149 <li>cleanup, especially memory wise</li>
150 <li>the parser should be more reliable, especially the HTML one, it should
151 not crash, whatever the input !</li>
152 <li>Integrated various patches, especially a speedup improvement for large
153 dataset from <a href="mailto:cnygard@bellatlantic.net">Carl Nygard</a>,
154 configure with --with-buffers to enable them.</li>
155 <li>attribute normalization, oops should have been added long ago !</li>
156 <li>attributes defaulted from Dtds should be available, xmlSetProp() now
157 does entities escapting by default.</li>
Daniel Veillard4c3a2031999-11-19 17:46:26 +0000[diff] [blame]158</ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]159
160<h3>1.7.4: Oct 25 1999</h3>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]161<ul>
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]162 <li>Lots of HTML improvement</li>
163 <li>Fixed some errors when saving both XML and HTML</li>
164 <li>More examples, the regression tests should now look clean</li>
165 <li>Fixed a bug with contiguous charref</li>
166</ul>
167
168<h3>1.7.3: Sep 29 1999</h3>
169<ul>
170 <li>portability problems fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]171 <li>snprintf was used unconditionnally, leading to link problems on system
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]172 were it's not available, fixed</li>
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]173</ul>
174
175<h3>1.7.1: Sep 24 1999</h3>
176<ul>
177 <li>The basic type for strings manipulated by libxml has been renamed in
178 1.7.1 from <strong>CHAR</strong> to <strong>xmlChar</strong>. The reason
179 is that CHAR was conflicting with a predefined type on Windows. However on
180 non WIN32 environment, compatibility is provided by the way of a
181 <strong>#define </strong>.</li>
182 <li>Changed another error : the use of a structure field called errno, and
183 leading to troubles on platforms where it's a macro</li>
184</ul>
185
186<h3>1.7.0: sep 23 1999</h3>
187<ul>
188 <li>Added the ability to fetch remote DTD or parsed entities, see the <a
189 href="gnome-xml-nanohttp.html">nanohttp</a> module.</li>
190 <li>Added an errno to report errors by another mean than a simple printf
191 like callback</li>
192 <li>Finished ID/IDREF support and checking when validation</li>
193 <li>Serious memory leaks fixed (there is now a <a
194 href="gnome-xml-xmlmemory.html">memory wrapper</a> module)</li>
195 <li>Improvement of <a href="http://www.w3.org/TR/xpath">XPath</a>
196 implementation</li>
197 <li>Added an HTML parser front-end</li>
198</ul>
199
200<h2><a name="XML">XML</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]201
202<p><a href="http://www.w3.org/TR/REC-xml">XML is a standard</a> for markup
203based structured documents, here is <a name="example">an example</a>:</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]204<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]205&lt;EXAMPLE prop1="gnome is great" prop2="&amp;amp; linux too">
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]206 &lt;head>
207 &lt;title>Welcome to Gnome&lt;/title>
208 &lt;/head>
209 &lt;chapter>
210 &lt;title>The Linux adventure&lt;/title>
211 &lt;p>bla bla bla ...&lt;/p>
212 &lt;image href="linus.gif"/>
213 &lt;p>...&lt;/p>
214 &lt;/chapter>
215&lt;/EXAMPLE></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]216
217<p>The first line specify that it's an XML document and gives useful
218informations about it's encoding. Then the document is a text format whose
219structure is specified by tags between brackets. <strong>Each tag opened have
220to be closed</strong> XML is pedantic about this, not that for example the
221image tag has no content (just an attribute) and is closed by ending up the
222tag with <code>/></code>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]223
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]224<p>XML can be applied sucessfully to a wide range or usage from long term
225structured document maintenance where it follows the steps of SGML to simple
226data encoding mechanism like configuration file format (glade), spreadsheets
227(gnumeric), or even shorter lived document like in WebDAV where it is used to
228encode remote call between a client and a server.</p>
229
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]230<h2><a name="tree">The tree output</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]231
232<p>The parser returns a tree built during the document analysis. The value
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]233returned is an <strong>xmlDocPtr</strong> (i.e. a pointer to an
234<strong>xmlDoc</strong> structure). This structure contains informations like
235the file name, the document type, and a <strong>root</strong> pointer which
236is the root of the document (or more exactly the first child under the root
237which is the document). The tree is made of <strong>xmlNode</strong>s, chained
238in double linked lists of siblings and with childs&lt;->parent relationship.
239An xmlNode can also carry properties (a chain of xmlAttr structures). An
240attribute 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]241
242<p>Here is an example (erroneous w.r.t. the XML spec since there should be
243only one ELEMENT under the root):</p>
244
245<p><img src="structure.gif" alt=" structure.gif "></p>
246
247<p>In the source package there is a small program (not installed by default)
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]248called <strong>tester</strong> which parses XML files given as argument and
249prints them back as parsed, this is useful to detect errors both in XML code
250and in the XML parser itself. It has an option <strong>--debug</strong> which
251prints the actual in-memory structure of the document, here is the result with
252the <a href="#example">example</a> given before:</p>
253<pre>DOCUMENT
254version=1.0
255standalone=true
256 ELEMENT EXAMPLE
257 ATTRIBUTE prop1
258 TEXT
259 content=gnome is great
260 ATTRIBUTE prop2
261 ENTITY_REF
262 TEXT
263 content= too
264 ELEMENT head
265 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]266 TEXT
267 content=Welcome to Gnome
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]268 ELEMENT chapter
269 ELEMENT title
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]270 TEXT
271 content=The Linux adventure
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]272 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]273 TEXT
274 content=bla bla bla ...
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]275 ELEMENT image
276 ATTRIBUTE href
277 TEXT
278 content=linus.gif
279 ELEMENT p
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]280 TEXT
281 content=...</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]282
283<p>This should be useful to learn the internal representation model.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]284
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]285<h2><a name="interface">The SAX interface</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]286
287<p>Sometimes the DOM tree output is just to large to fit reasonably into
288memory. In that case and if you don't expect to save back the XML document
289loaded using libxml, it's better to use the SAX interface of libxml. SAX is a
290<strong>callback based interface</strong> to the parser. Before parsing, the
291application layer register a customized set of callbacks which will be called
292by the library as it progresses through the XML input.</p>
293
294<p>To get a more detailed step-by-step guidance on using the SAX interface of
295libxml, <a href="mailto:james@daa.com.au">James Henstridge</a> made <a
296href="http://www.daa.com.au/~james/gnome/xml-sax/xml-sax.html">a nice
297documentation.</a></p>
298
299<p>You can debug the SAX behaviour by using the <strong>testSAX</strong>
300program located in the gnome-xml module (it's usually not shipped in the
301binary packages of libxml, but you can also find it in the tar source
302distribution). Here is the sequence of callback that would be generated when
303parsing the example given before as reported by testSAX:</p>
304<pre>SAX.setDocumentLocator()
305SAX.startDocument()
306SAX.getEntity(amp)
307SAX.startElement(EXAMPLE, prop1='gnome is great', prop2='&amp;amp; linux too')
308SAX.characters( , 3)
309SAX.startElement(head)
310SAX.characters( , 4)
311SAX.startElement(title)
312SAX.characters(Welcome to Gnome, 16)
313SAX.endElement(title)
314SAX.characters( , 3)
315SAX.endElement(head)
316SAX.characters( , 3)
317SAX.startElement(chapter)
318SAX.characters( , 4)
319SAX.startElement(title)
320SAX.characters(The Linux adventure, 19)
321SAX.endElement(title)
322SAX.characters( , 4)
323SAX.startElement(p)
324SAX.characters(bla bla bla ..., 15)
325SAX.endElement(p)
326SAX.characters( , 4)
327SAX.startElement(image, href='linus.gif')
328SAX.endElement(image)
329SAX.characters( , 4)
330SAX.startElement(p)
331SAX.characters(..., 3)
332SAX.endElement(p)
333SAX.characters( , 3)
334SAX.endElement(chapter)
335SAX.characters( , 1)
336SAX.endElement(EXAMPLE)
337SAX.endDocument()</pre>
338
339<p>Most of the other functionnalities of libxml are based on the DOM tree
340building facility, so nearly everything up to the end of this document
341presuppose the use of the standard DOM tree build. Note that the DOM tree
342itself is built by a set of registered default callbacks, without internal
343specific interface.</p>
344
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]345<h2><a name="library">The XML library interfaces</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]346
347<p>This section is directly intended to help programmers getting bootstrapped
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]348using the XML library from the C language. It doesn't intent to be extensive,
349I hope the automatically generated docs will provide the completeness
350required, but as a separated set of documents. The interfaces of the XML
351library are by principle low level, there is nearly zero abstration. Those
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]352interested in a higher level API should <a href="#DOM">look at DOM</a>.</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]353
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]354<h3><a name="Invoking">Invoking the parser</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]355
356<p>Usually, the first thing to do is to read an XML input, the parser accepts
357to parse both memory mapped documents or direct files. The functions are
358defined in "parser.h":</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]359<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]360 <dt><code>xmlDocPtr xmlParseMemory(char *buffer, int size);</code></dt>
361 <dd><p>parse a zero terminated string containing the document</p>
362 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]363</dl>
364<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]365 <dt><code>xmlDocPtr xmlParseFile(const char *filename);</code></dt>
366 <dd><p>parse an XML document contained in a file (possibly compressed)</p>
367 </dd>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]368</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]369
370<p>This returns a pointer to the document structure (or NULL in case of
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]371failure).</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]372
373<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]374memory-hungry, first to load the document in memory, second to build the tree.
375Reading a document without building the tree will be possible in the future by
376pluggin the code to the SAX interface (see SAX.c).</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]377
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]378<h3><a name="Building">Building a tree from scratch</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]379
380<p>The other way to get an XML tree in memory is by building it. Basically
381there is a set of functions dedicated to building new elements, those are also
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]382described in "tree.h", here is for example the piece of code producing the
383example used before:</p>
384<pre> xmlDocPtr doc;
385 xmlNodePtr tree, subtree;
386
387 doc = xmlNewDoc("1.0");
388 doc->root = xmlNewDocNode(doc, NULL, "EXAMPLE", NULL);
389 xmlSetProp(doc->root, "prop1", "gnome is great");
390 xmlSetProp(doc->root, "prop2", "&amp;linux; too");
391 tree = xmlNewChild(doc->root, NULL, "head", NULL);
392 subtree = xmlNewChild(tree, NULL, "title", "Welcome to Gnome");
393 tree = xmlNewChild(doc->root, NULL, "chapter", NULL);
394 subtree = xmlNewChild(tree, NULL, "title", "The Linux adventure");
395 subtree = xmlNewChild(tree, NULL, "p", "bla bla bla ...");
396 subtree = xmlNewChild(tree, NULL, "image", NULL);
397 xmlSetProp(subtree, "href", "linus.gif");</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]398
399<p>Not really rocket science ...</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]400
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]401<h3><a name="Traversing">Traversing the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]402
403<p>Basically by including "tree.h" your code has access to the internal
404structure of all the element of the tree. The names should be somewhat simple
405like <strong>parent</strong>, <strong>childs</strong>, <strong>next</strong>,
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]406<strong>prev</strong>, <strong>properties</strong>, etc... For example still
407with the previous example:</p>
408<pre><code>doc->root->childs->childs</code></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]409
410<p>points to the title element,</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]411<pre>doc->root->childs->next->child->child</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]412
413<p>points to the text node containing the chapter titlle "The Linux adventure"
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]414and</p>
415<pre>doc->root->properties->next->val</pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]416
417<p>points to the entity reference containing the value of "&amp;linux" at the
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]418beginning of the second attribute of the root element "EXAMPLE".</p>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]419
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]420<p><strong>NOTE</strong>: XML allows <em>PI</em>s and <em>comments</em> to be
421present before the document root, so doc->root may point to an element which
422is not the document Root Element, a function
423<code>xmlDocGetRootElement()</code> was added for this purpose. </p>
424
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]425<h3><a name="Modifying">Modifying the tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]426
427<p>functions are provided to read and write the document content:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]428<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]429 <dt><code>xmlAttrPtr xmlSetProp(xmlNodePtr node, const xmlChar *name, const
430 xmlChar *value);</code></dt>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]431 <dd><p>This set (or change) an attribute carried by an ELEMENT node the
432 value can be NULL</p>
433 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]434</dl>
435<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]436 <dt><code>const xmlChar *xmlGetProp(xmlNodePtr node, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]437 *name);</code></dt>
438 <dd><p>This function returns a pointer to the property content, note that
439 no extra copy is made</p>
440 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]441</dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]442
443<p>Two functions must be used to read an write the text associated to
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]444elements:</p>
445<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]446 <dt><code>xmlNodePtr xmlStringGetNodeList(xmlDocPtr doc, const xmlChar
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]447 *value);</code></dt>
448 <dd><p>This function takes an "external" string and convert it to one text
449 node or possibly to a list of entity and text nodes. All non-predefined
450 entity references like &amp;Gnome; will be stored internally as an
451 entity node, hence the result of the function may not be a single
452 node.</p>
453 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]454</dl>
455<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]456 <dt><code>xmlChar *xmlNodeListGetString(xmlDocPtr doc, xmlNodePtr list, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]457 inLine);</code></dt>
458 <dd><p>this is the dual function, which generate a new string containing
459 the content of the text and entity nodes. Note the extra argument
460 inLine, if set to 1 instead of returning the &amp;Gnome; XML encoding in
461 the string it will substitute it with it's value say "GNU Network Object
462 Model Environment". Set it if you want to use the string for non XML
463 usage like User Interface.</p>
464 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]465</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]466
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]467<h3><a name="Saving">Saving a tree</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]468
469<p>Basically 3 options are possible:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]470<dl>
Daniel Veillarddd6b3671999-09-23 22:19:22 +0000[diff] [blame]471 <dt><code>void xmlDocDumpMemory(xmlDocPtr cur, xmlChar**mem, int
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]472 *size);</code></dt>
473 <dd><p>returns a buffer where the document has been saved</p>
474 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]475</dl>
476<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]477 <dt><code>extern void xmlDocDump(FILE *f, xmlDocPtr doc);</code></dt>
478 <dd><p>dumps a buffer to an open file descriptor</p>
479 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]480</dl>
481<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]482 <dt><code>int xmlSaveFile(const char *filename, xmlDocPtr cur);</code></dt>
483 <dd><p>save the document ot a file. In that case the compression interface
484 is triggered if turned on</p>
485 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]486</dl>
Daniel Veillard10c6a8f1998-10-28 01:00:12 +0000[diff] [blame]487
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]488<h3><a name="Compressio">Compression</a></h3>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]489
490<p>The library handle transparently compression when doing file based
491accesses, the level of compression on saves can be tuned either globally or
492individually for one file:</p>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]493<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]494 <dt><code>int xmlGetDocCompressMode (xmlDocPtr doc);</code></dt>
495 <dd><p>Get the document compression ratio (0-9)</p>
496 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]497</dl>
498<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]499 <dt><code>void xmlSetDocCompressMode (xmlDocPtr doc, int mode);</code></dt>
500 <dd><p>Set the document compression ratio</p>
501 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]502</dl>
503<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]504 <dt><code>int xmlGetCompressMode(void);</code></dt>
505 <dd><p>Get the default compression ratio</p>
506 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]507</dl>
508<dl>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]509 <dt><code>void xmlSetCompressMode(int mode);</code></dt>
510 <dd><p>set the default compression ratio</p>
511 </dd>
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]512</dl>
513
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]514<h2><a name="Entities">Entities or no entities</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]515
516<p>Entities principle is similar to simple C macros. They define an
517abbreviation for a given string that you can reuse many time through the
518content of your document. They are especially useful when frequent occurrences
519of a given string may occur within a document or to confine the change needed
520to a document to a restricted area in the internal subset of the document (at
521the beginning). Example:</p>
522<pre>1 &lt;?xml version="1.0"?>
5232 &lt;!DOCTYPE EXAMPLE SYSTEM "example.dtd" [
5243 &lt;!ENTITY xml "Extensible Markup Language">
5254 ]>
5265 &lt;EXAMPLE>
5276 &amp;xml;
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]5287 &lt;/EXAMPLE></pre>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]529
530<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]531it's name with '&amp;' and following it by ';' without any spaces added. There
532are 5 predefined entities in libxml allowing to escape charaters with
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]533predefined meaning in some parts of the xml document content:
534<strong>&amp;lt;</strong> for the letter '&lt;', <strong>&amp;gt;</strong> for
535the letter '>', <strong>&amp;apos;</strong> for the letter ''',
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]536<strong>&amp;quot;</strong> for the letter '"', and <strong>&amp;amp;</strong>
537for the letter '&amp;'.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]538
539<p>One of the problems related to entities is that you may want the parser to
540substitute entities content to see the replacement text in your application,
541or you may prefer keeping entities references as such in the content to be
542able to save the document back without loosing this usually precious
543information (if the user went through the pain of explicitley defining
544entities, he may have a a rather negative attitude if you blindly susbtitute
545them as saving time). The function <a
546href="gnome-xml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a>
547allows to check and change the behaviour, which is to not substitute entities
548by default.</p>
549
550<p>Here is the DOM tree built by libxml for the previous document in the
551default case:</p>
552<pre>/gnome/src/gnome-xml -> ./tester --debug test/ent1
553DOCUMENT
554version=1.0
555 ELEMENT EXAMPLE
556 TEXT
557 content=
558 ENTITY_REF
559 INTERNAL_GENERAL_ENTITY xml
560 content=Extensible Markup Language
561 TEXT
562 content=</pre>
563
564<p>And here is the result when substituting entities:</p>
565<pre>/gnome/src/gnome-xml -> ./tester --debug --noent test/ent1
566DOCUMENT
567version=1.0
568 ELEMENT EXAMPLE
569 TEXT
570 content= Extensible Markup Language</pre>
571
572<p>So entities or no entities ? Basically it depends on your use case, I
573suggest to keep the non-substituting default behaviour and avoid using
574entities in your XML document or data if you are not willing to handle the
575entity references elements in the DOM tree.</p>
576
577<p>Note that at save time libxml enforce the conversion of the predefined
578entities where necessary to prevent well-formedness problems, and will also
579transparently replace those with chars (i.e. will not generate entity
580reference elements in the DOM tree nor call the reference() SAX callback when
581finding them in the input).</p>
582
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]583<h2><a name="Namespaces">Namespaces</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]584
585<p>The libxml library implement namespace @@ support by recognizing namespace
586contructs in the input, and does namespace lookup automatically when building
587the DOM tree. A namespace declaration is associated with an in-memory
588structure and all elements or attributes within that namespace point to it.
589Hence testing the namespace is a simple and fast equality operation at the
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]590user level.</p>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]591
592<p>I suggest it that people using libxml use a namespace, and declare it on
593the root element of their document as the default namespace. Then they dont
594need to happend the prefix in the content but we will have a basis for future
595semantic refinement and merging of data from different sources. This doesn't
596augment significantly the size of the XML output, but significantly increase
597it's value in the long-term.</p>
598
599<p>Concerning the namespace value, this has to be an URL, but this doesn't
600have to point to any existing resource on the Web. I suggest using an URL
601within a domain you control, which makes sense and if possible holding some
602kind of versionning informations. For example
603<code>"http://www.gnome.org/gnumeric/1.0"</code> is a good namespace scheme.
604Then when you load a file, make sure that a namespace carrying the
605version-independant prefix is installed on the root element of your document,
606and if the version information don't match something you know, warn the user
607and be liberal in what you accept as the input. Also do *not* try to base
608namespace checking on the prefix value &lt;foo:text> may be exactly the same
609as &lt;bar:text> in another document, what really matter is the URI
610associated with the element or the attribute, not the prefix string which is
611just a shortcut for the full URI.</p>
612
613<p>@@Interfaces@@</p>
614
615<p>@@Examples@@</p>
616
617<p>Usually people object using namespace in the case of validation, I object
618this and will make sure that using namespaces won't break validity checking,
619so even is you plan or are using validation I strongly suggest to add
620namespaces to your document. A default namespace scheme
621<code>xmlns="http://...."</code> should not break validity even on less
622flexible parsers. Now using namespace to mix and differenciate content coming
623from mutliple Dtd will certainly break current validation schemes, I will try
624to provide ways to do this, but this may not be portable or standardized.</p>
625
Daniel Veillard2f4dfc41999-09-24 14:03:48 +0000[diff] [blame]626<h2><a name="Validation">Validation, or are you afraid of DTDs ?</a></h2>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]627
628<p>Well what is validation and what is a DTD ?</p>
629
630<p>Validation is the process of checking a document against a set of
631construction rules, a <strong>DTD</strong> (Document Type Definition) is such
632a set of rules.</p>
633
634<p>The validation process and building DTDs are the two most difficult parts
635of XML life cycle. Briefly a DTD defines all the possibles element to be
636found within your document, what is the formal shape of your document tree (by
637defining the allowed content of an element, either text, a regular expression
638for the allowed list of children, or mixed content i.e. both text and childs).
639The DTD also defines the allowed attributes for all elements and the types of
640the attributes. For more detailed informations, I suggest to read the related
641parts of the XML specification, the examples found under
642gnome-xml/test/valid/dtd and the large amount of books available on XML. The
643dia example in gnome-xml/test/valid should be both simple and complete enough
644to allow you to build your own.</p>
645
646<p>A word of warning, building a good DTD which will fit your needs of your
647application in the long-term is far from trivial, however the extra level of
648quality it can insure is well worth the price for some sets of applications or
649if you already have already a DTD defined for your application field.</p>
650
651<p>The validation is not completely finished but in a (very IMHO) usable
652state. Until a real validation interface is defined the way to do it is to
653define and set the <strong>xmlDoValidityCheckingDefaultValue</strong> external
654variable to 1, this will of course be changed at some point:</p>
655
656<p>extern int xmlDoValidityCheckingDefaultValue;</p>
657
658<p>...</p>
659
660<p>xmlDoValidityCheckingDefaultValue = 1;</p>
661
662<p></p>
663
664<p>To handle external entities, use the function
665<strong>xmlSetExternalEntityLoader</strong>(xmlExternalEntityLoader f); to
666link in you HTTP/FTP/Entities database library to the standard libxml
667core.</p>
668
669<p>@@interfaces@@</p>
670
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]671<h2><a name="DOM"></a><a name="Principles">DOM Principles</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]672
673<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]674Model</em> this is an API for accessing XML or HTML structured documents.
675Native 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]676be based on gnome-xml. This will be a far cleaner interface to manipulate XML
Daniel Veillardc08a2c61999-09-08 21:35:25 +0000[diff] [blame]677files within Gnome since it won't expose the internal structure. DOM defines a
Daniel Veillard25940b71998-10-29 05:51:30 +0000[diff] [blame]678set of IDL (or Java) interfaces allowing to traverse and manipulate a
679document. The DOM library will allow accessing and modifying "live" documents
680presents on other programs like this:</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]681
682<p><img src="DOM.gif" alt=" DOM.gif "></p>
683
684<p>This should help greatly doing things like modifying a gnumeric spreadsheet
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]685embedded in a GWP document for example.</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]686
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]687<p>The current DOM implementation on top of libxml is the <a
688href="http://cvs.gnome.org/lxr/source/gdome/">gdome Gnome module</a>, this is
689a full DOM interface, thanks to <a href="mailto:raph@levien.com">Raph
690Levien</a>.</p>
691
692<p>The gnome-dom module in the Gnome CVS base is obsolete</p>
693
Daniel Veillard35008381999-10-25 13:15:52 +0000[diff] [blame]694<h2><a name="Example"></a><a name="real">A real example</a></h2>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]695
696<p>Here is a real size example, where the actual content of the application
697data 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]698a proposal to keep a database of jobs related to Gnome, with an XML based
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]699storage structure. Here is an <a href="gjobs.xml">XML encoded jobs
700base</a>:</p>
701<pre>&lt;?xml version="1.0"?>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]702&lt;gjob:Helping xmlns:gjob="http://www.gnome.org/some-location">
703 &lt;gjob:Jobs>
704
705 &lt;gjob:Job>
706 &lt;gjob:Project ID="3"/>
707 &lt;gjob:Application>GBackup&lt;/gjob:Application>
708 &lt;gjob:Category>Development&lt;/gjob:Category>
709
710 &lt;gjob:Update>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]711 &lt;gjob:Status>Open&lt;/gjob:Status>
712 &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]713 &lt;gjob:Salary>USD 0.00&lt;/gjob:Salary>
714 &lt;/gjob:Update>
715
716 &lt;gjob:Developers>
717 &lt;gjob:Developer>
718 &lt;/gjob:Developer>
719 &lt;/gjob:Developers>
720
721 &lt;gjob:Contact>
722 &lt;gjob:Person>Nathan Clemons&lt;/gjob:Person>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]723 &lt;gjob:Email>nathan@windsofstorm.net&lt;/gjob:Email>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]724 &lt;gjob:Company>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]725 &lt;/gjob:Company>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]726 &lt;gjob:Organisation>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]727 &lt;/gjob:Organisation>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]728 &lt;gjob:Webpage>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]729 &lt;/gjob:Webpage>
730 &lt;gjob:Snailmail>
731 &lt;/gjob:Snailmail>
732 &lt;gjob:Phone>
733 &lt;/gjob:Phone>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]734 &lt;/gjob:Contact>
735
736 &lt;gjob:Requirements>
737 The program should be released as free software, under the GPL.
738 &lt;/gjob:Requirements>
739
740 &lt;gjob:Skills>
741 &lt;/gjob:Skills>
742
743 &lt;gjob:Details>
744 A GNOME based system that will allow a superuser to configure
745 compressed and uncompressed files and/or file systems to be backed
746 up with a supported media in the system. This should be able to
747 perform via find commands generating a list of files that are passed
748 to tar, dd, cpio, cp, gzip, etc., to be directed to the tape machine
749 or via operations performed on the filesystem itself. Email
750 notification and GUI status display very important.
751 &lt;/gjob:Details>
752
753 &lt;/gjob:Job>
754
755 &lt;/gjob:Jobs>
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]756&lt;/gjob:Helping></pre>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]757
758<p>While loading the XML file into an internal DOM tree is a matter of calling
759only a couple of functions, browsing the tree to gather the informations and
760generate the internals structures is harder, and more error prone.</p>
761
762<p>The suggested principle is to be tolerant with respect to the input
763structure. For example the ordering of the attributes is not significant, Cthe
764XML specification is clear about it. It's also usually a good idea to not be
765dependant of the orders of the childs of a given node, unless it really makes
766things harder. Here is some code to parse the informations for a person:</p>
767<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]768 * A person record
769 */
770typedef struct person {
771 char *name;
772 char *email;
773 char *company;
774 char *organisation;
775 char *smail;
776 char *webPage;
777 char *phone;
778} person, *personPtr;
779
780/*
781 * And the code needed to parse it
782 */
783personPtr parsePerson(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
784 personPtr ret = NULL;
785
786DEBUG("parsePerson\n");
787 /*
788 * allocate the struct
789 */
790 ret = (personPtr) malloc(sizeof(person));
791 if (ret == NULL) {
792 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]793 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]794 }
795 memset(ret, 0, sizeof(person));
796
797 /* We don't care what the top level element name is */
798 cur = cur->childs;
799 while (cur != NULL) {
800 if ((!strcmp(cur->name, "Person")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]801 ret->name = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]802 if ((!strcmp(cur->name, "Email")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]803 ret->email = xmlNodeListGetString(doc, cur->childs, 1);
804 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]805 }
806
807 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]808}</pre>
809
810<p>Here is a couple of things to notice:</p>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]811<ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]812 <li>Usually a recursive parsing style is the more convenient one, XML data
813 being by nature subject to repetitive constructs and usualy exibit highly
814 stuctured patterns.</li>
815 <li>The two arguments of type <em>xmlDocPtr</em> and <em>xmlNsPtr</em>, i.e.
816 the pointer to the global XML document and the namespace reserved to the
817 application. Document wide information are needed for example to decode
818 entities and it's a good coding practice to define a namespace for your
819 application set of data and test that the element and attributes you're
820 analyzing actually pertains to your application space. This is done by a
821 simple equality test (cur->ns == ns).</li>
822 <li>To retrieve text and attributes value, it is suggested to use the
823 function <em>xmlNodeListGetString</em> to gather all the text and entity
824 reference nodes generated by the DOM output and produce an single text
825 string.</li>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]826</ul>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]827
828<p>Here is another piece of code used to parse another level of the
829structure:</p>
830<pre>/*
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]831 * a Description for a Job
832 */
833typedef struct job {
834 char *projectID;
835 char *application;
836 char *category;
837 personPtr contact;
838 int nbDevelopers;
839 personPtr developers[100]; /* using dynamic alloc is left as an exercise */
840} job, *jobPtr;
841
842/*
843 * And the code needed to parse it
844 */
845jobPtr parseJob(xmlDocPtr doc, xmlNsPtr ns, xmlNodePtr cur) {
846 jobPtr ret = NULL;
847
848DEBUG("parseJob\n");
849 /*
850 * allocate the struct
851 */
852 ret = (jobPtr) malloc(sizeof(job));
853 if (ret == NULL) {
854 fprintf(stderr,"out of memory\n");
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]855 return(NULL);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]856 }
857 memset(ret, 0, sizeof(job));
858
859 /* We don't care what the top level element name is */
860 cur = cur->childs;
861 while (cur != NULL) {
862
863 if ((!strcmp(cur->name, "Project")) &amp;&amp; (cur->ns == ns)) {
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]864 ret->projectID = xmlGetProp(cur, "ID");
865 if (ret->projectID == NULL) {
866 fprintf(stderr, "Project has no ID\n");
867 }
868 }
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]869 if ((!strcmp(cur->name, "Application")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]870 ret->application = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]871 if ((!strcmp(cur->name, "Category")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]872 ret->category = xmlNodeListGetString(doc, cur->childs, 1);
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]873 if ((!strcmp(cur->name, "Contact")) &amp;&amp; (cur->ns == ns))
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]874 ret->contact = parsePerson(doc, ns, cur);
875 cur = cur->next;
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]876 }
877
878 return(ret);
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]879}</pre>
Daniel Veillard14fff061999-06-22 21:49:07 +0000[diff] [blame]880
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]881<p>One can notice that once used to it, writing this kind of code is quite
882simple, but boring. Ultimately, it could be possble to write stubbers taking
883either C data structure definitions, a set of XML examples or an XML DTD and
884produce the code needed to import and export the content between C data and
885XML storage. This is left as an exercise to the reader :-)</p>
886
887<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]888example</a> as a template, it is also available with Makefile in the Gnome CVS
889base under gnome-xml/example</p>
Daniel Veillardb05deb71999-08-10 19:04:08 +0000[diff] [blame]890
Daniel Veillardc8eab3a1999-09-04 18:27:23 +0000[diff] [blame]891<p></p>
892
893<p><a href="mailto:Daniel.Veillard@w3.org">Daniel Veillard</a></p>
894
Daniel Veillardb24054a1999-12-18 15:32:46 +0000[diff] [blame]895<p>$Id: xml.html,v 1.15 1999/12/18 15:32:46 veillard Exp $</p>
Daniel Veillardccb09631998-10-27 06:21:04 +0000[diff] [blame]896</body>
897</html>